What would it take to use a 103 motor in an '01 Ultra Classic?
 

I have an 88TC right now, stock. New A/C, about to put an exhaust on. This 88TC only has 29000 miles, and I'm going to ride it until it needs a rebuild, then likely either sell it or keep it as a spare.
Figure instead of a big bore kit for a couple thousand, why not spend a couple thousand on a used 103, and while it's out, rebuild, cams, any other modifications I want to make. Seems like a better bang for my buck than a big bore for the 88.

I haven't seen a 103 on a touring bike, so not sure what the difference is. Is it too big for the '01 touring frame? Heard it may require fabrication.
Most guys I know with touring bikes either have new, so Milwaukee, or old like mine.

I know I can get a used 103 for about $1700, used six speed for about $600. Would likely rebuild both of those.

I understand why anyone would build an engine of choice while still running what they already have but remember if you put your trust in this used 103 you are taking a chance. A lesson I learned in doing upgrades to my 06 electra 88 TC is that taking baby steps actually cost me more than if I had jumped right in and built the engine I really preferred right out of the gate. First I did a stage one then came cams, then when I went to increase bore to a 96" a couple of seasons later, I ended up with a sad face. The whimpy Harley crank apparently couldn't take the upgrades and was failing. So in went to a 4.375 S&S crank,585 cams and bored to 3.875 creating a 103. Good engine but If I had known I would end up craving more HP and cubes (it's a fever), I would not have done all this in baby steps and I'd likely have gone straight to something with even more cubes, I'm getting hungry for more---again! But in the next breath, I realize most of us do have a budget limiting us.

You have a 2001 so good crank with the Timken bearing...I wouldn't trade that for a newer 103 to swap that's for sure. Besides the numbers not matching it's just a big ol can of worms to open. You'll need the transmission, primary at least and likely any electrical crap needed to make it run...ie the ecm? Check your runout because you can probably run gear driven cams and then go 98"...how much power are you looking for? If a good running 98 isn't enough it's going to get expensive to bigger than that...Besides the s&s 100" kit. Sure is fun running away from a guy with a " bigger" engine than you lol.

anything fits with some mods

You can fit the later 103 motor and tranny into the earlier frame but it has to be for a bagger and you'll have to use the later primary / starter.

I was debating this same swap minus the 6 speed though. Will a 103 engine bolt to a 2006 EG with a five speed and the 06 primary?

This,forged lower end too vs cast.
Do a bore kit with a bump in compression and gear drive cams maybe ported heads and she'll not only run like a scalded dog she'll run 'til the cows come home.

Nope. Do more research..

However, all that said, you can do a lot of things if you happen to be a talented machine shop with free time and or cubic $$$$.
I am neither :D

You could however, rebuild your 06 TC88 into a 103 with a new crank and pistons and other parts. But as has been said, you cannot swap a 07-up motor to a 06- earlier transmission/primary.