Welcome to the forum. H-D began using SNs on frames for either 1916 or 17 and kept using them thru 1927 models but then they stopped using them for a long time.
Beginning with 1962 models (maybe 61 models?), certain H-D frames were stamped with an additional original component identifying number (AOCIN), aka security code, aka anti-theft number and this continued thru 69. An AOCIN was also stamped on some 70 model frames even though they had a VIN.

Shiny frame has a front engine mount I’m not sure about yet. In your photo below are there any markings in the three areas I outlined in red? And can you post a close-up of the area outlined in blue please.






R-H side of the brake crossover shaft tube has been removed and so has its support. Later somebody put on the bracket I outlined in orange.
Original footboard stud tabs were removed and somebody put other types on later.
Sidecar loops have been removed. Etc.

As mentioned above, your other frame was originally a swingarm model and someone added a hardtail to it. Notice the left axle clip extends below the frame tube and the large hole in the clip accommodates the anchor stud of a hydraulic drum brake.
R-H side of the steering head looks like it has forging die number 31? If 31 it indicates the steering head is a 58 or 59 model. Next to it is forging hallmark DIF representing Interstate Drop Forge.
On the R-H side of the top engine mount you may find a date code consisting of a letter and a number. Letter indicates month of manufacture and number indicates year. Looks like something is there? Perhaps the letter I?
At the back of the front engine mount you may find forging number 47664-48 and a forging hallmark consisting of M over F (Modern Drop Forge) inside a circle. And a forging die number that may be about 3?
Both footboard stud tabs have been removed.
Assigned identification number tag on the left front downtube.
Carb cable clamp tab has been removed from under the stress bar. Etc.

Notice the vent screw thru the trans lid. It was first placed in that position for 56 models. But the lid is 59-later because it has a switch. The lid may even be 65-later due in part to its countersunk socket-head screws.
For 40–55 models (and maybe very late 39s) the trans normally had a vent nipple thru a boss in the top of the case but I don’t see a boss on top of your case. Has it got one? Photo?

I can’t see anything wrong with the engine SN and all characters appear normal factory types for a 46 Knuckle. SNs for 46 began at 1000 and 7376 is within the accepted range.
Belly numbers may begin with 46-. But some very late 46 models had belly numbers beginning with 47- so if yours do could you let us know. Thanks.
Eric

 

Amazing knowledge you have sir...! Please see the attached images for the shiny frame. I was able to locate more numbers. I used some acetone to get past the paint on the axle tabs. Question is now is the frame 100% original? I will post the rusty frame soon again.

Front bracing number.

What makes a wishbone frame? Is it the flared tubing in the front like the image?

Axle tab number right side.

This has a stamped I letter as apposed to the X in the rusty frame.







Axle tab number right side.

Axle tab number left side.

 

XE-7 10 is 1948 on the left axle clip, a 48 frame thats been modified. If the upper engine mount is original to the frame then its an early 48 frame. Other die numbers may narrow it down as well.

 

Grind the side of the upper engine mount to get it down to steel to see if its flat or if someone filled in around the rib.

 

Took all the paint off and it's definitely steel. Is this what you were wanting?

 

You need to clean that tab down to the metal entirely to see if its a flat tab or one with a raised hump in it.

 

 

It's a late 48 frame. The rib is clear in the middle of the bracket where it meets the frame.

The die number 10 on the axle clip is still 1948 but approaching 1949 which jives with the rib on the mount.

The underside of the upper seat post forging will have a number. The other axle clip will have a number as well. Its safe to assume the lower seat post forging is original because of how difficult it would be to replace.

 

The down side to your 48 frame is the axle clips have been trimmed where the rear stand is, Tool box bracket cut off, Rear brake cross shaft tube cut off, side car loops cut off and smoothed over and the worst part is what was done to the neck forging. It's an expensive frame but very expensive to return to stock.

 

Thanks for the extra photos. Yes it's called a wishbone frame because of the front downtubes. If they were straight the frame would be called a straight leg. WB frames were used for 1948 thru about mid-54.

Re the area on the R-H side where the brake pedal bracket goes, markings there are something I continue to investigate. In this instance the letter I may just be an inspector marking.

Reinforcement of that type of top engine mount indicates later-48 thru 51.

Your front engine mount has forging number 48E-621 which was used for 48–57. It also appears to have a forging die number which may be 2? If so it suggests the front mount is 49–50. Next to the die number is a forging hallmark which probably consists of letters M over F in a circle which represents Modern Drop Forge, the maker of the mount. Here’s your photo. Can you confirm if the die number is 2? To the other side the area I outlined in blue looks filled in as opposed to being a channel?






Next is another of your photos and it too shows that area filled in. Does that area look original to the forging?





I can’t see any markings under the seat post forging. Under one side you may find forging number 48E-1. Under the opposite side you may find forging hallmark M over F and a die number which may be 2 or 3? Photo?
Also look on top of the seat post forging. If a frame was sent in for repair the factory stamped a number on top. Photo?

At the back of the rear engine mount you may find forging number XE-624, forging hallmark DIF and a die number which may be about 5 or 6? Here’s an example with 5.





Your R-H axle clip has forging number XE-6 and hallmark DIF. But what is the die number? Is it 7 or could it be something else?
Eric