Welcome! Nice bike- any better pics?
Gurls blouse cb900f rear shocks are 360mm eye to eye as aposed to yours (320ish mm) and will fit if you file the bush on the swingarm down by a mm or so.
Not sure how far you can go- but you could work it out using a piece of bar/timber to mock up max shock length before chain fouls.
Hi and Welcome.
I think some pics of progress so far would help inspire wheel suggestions
Also- All of @wraithsuggestions are going to be best for budget. B6/teapot stuff doesn’t cost huge amounts.