I just finished restoring a Balboa with the rare 1c . It needed a lot of work and was a project with my 16 year old grandson . It runs great now and does low 30s on flat ground . We don’t use the Decomp. You should get the Decomp issue resolved and get an accurate compression test . The cyl / head is one unit and easy to work on, ours had a piston with big hunks broken off the skirt. The carbs are finicky just clean it good and put the pieces back correctly. The clutch will probably need going over also.
Get a good repair manual take your time, They are very good bikes and that Balboa is one of the best looking out there.