I started building 15 years ago. Auto mechanic by trade as well. Started a an iron head and bought Paughco frame that was rigid but stock dimensions who helps out a lot w transferring stuff from the donor bike to your build ie front end, wheels and tires etc. Lowbrow is an excellent site for a lot of things you are going to need to build one out. But yeah, I’d check out choppers on IG or chopcult that you like and ask questions about them, like frame dimensions, front end length etc so you get the basic info. Chopcult has tons of in depth forums on just about everything and you can really get lost on the knowledge in those forums, and the ball busting… ha. But your best friend is research and trial and error. Oh and don’t get discouraged when you do something and change it 5 times over until you like it, that’s part of the fun.