I remember building up a Gold tank one for my Dad, in 1975 or there abouts.
Cost about $150, it had already been stripped of all the road gear.
We built a chamber for it, based on the MK4 Pursang pipe, but just a bit fatter and longer.
No Porting, but it actually worked pretty well.
A brand new seat from Yamaha was about $35. New Tank badges $7.50 ea. New 'fuzzy' Air filter about the same.
It already had a 21" front wheel (steel), (NSW ones were 19"?). We fitted 'Pacifico' plastic guards.
Second hand Knobbies ($5 ea)
Front forks were the steel ones, I put them in a lathe and knocked off all the brackets and "skimmed" them down a tiny bit.
Rear shocks were a problem in those days! Needed a road trip, from Geelong to Melbourne, following up an ad in REV's.
Bought a set of replacements (Japanese, chrome plated) for $40.
Not too embarrassing as a MX practice bike, and absolutely, totally reliable. Never touched the engine...ever.
Cheers, DJ