I like your idea, too. Just noticed the Sweden thing. Welcome to the forum.

 

Would suggest SE-204 cams, 50mm Throttle Body and CNC Machined heads. This setup will allow to maintain stock compression and with a good exhaust and AC will let u pass 100hp/150Nm which is pure fun...

 

Would SE-204 be a better choice Tham S&S 585?
Yes, ported heads with changed valves is now on the list instead of the 79cc heads
Regarding the TB I spoke to one of the most renowned tuners here in Sweden and according to him he never seen the use for a larger TB on a 107 engine. A to biG TB might even lead to degraded torque. I don't know what to think. I have seen many here that uses TB's between 50-55mm that thinks it's an improvement?
Regarding exhaust I will keep my big radius 2-2. I know that it is not the best regarding performance but I like the look and sound.

 

Theoretically a bigger throttle body increases hp BUT on a 103 with AC, exhaust, cams and ported heads a 50mm is simply the correct size. 2013/14/15 BO has a 46mm and 2016/17 High Output 103 uses 50mm...there must be a reason why...
Personally the 50mm tb on my setup improved the overall performance in terms of TQ and hp on the entire range of rpms.
Regarding SE-204 cams I can only say it has been one of the best mods made, bike completely changed the way it behaves and with a good dyno the result is simply awesome...

 

Cyclerama 575 cams, been a few really torque ripping builds on here lately. Worth a look especially with heads. Lots out there too choose from. I used the s&s mr103 cam only upgrade and it's great. Dyno sheet is in the softail dyno section.

 

I'll throw in my .02. I would keep my HD parts and modify them. Bore your stock cylinders out to 107 and use some CP pistons with 10.5 pistons. Get your stock heads worked over letting your porter know where you spend your time in the RPM range. The cam is the most important part to me because you need to match it to your riding style. TB size is an open subject and on my 107 I use a 55. If you like to twist up the reves the 625 mentioned would be ok but I like the 585 myself. I have a Woods tw5 if my mind is working right now. Case in point is I also have a 124" motor in a Fatboy. It rips but doesn't start working good till about 3500. Very seldom do I use it there. On the other hand my Crossbones with the 107 comes on in the lower 2's and is a hoot to ride. Crossbones is my favorite ride with it's tamer cam. this winter the Fatboy is getting a 585 for a lower RPM hit.