1985 Yamaha Tri-Z Forks and Engine advise
I don't know how mechanically inclined you are, but forks aren't difficult to rebuild yourself if you're capable and if the tubes are good. If you have some extra dough, a lot of guys go to inverts these days. The shock is best rebuilt by a professional though. I don't know about the Tri-Z's specifically, but many times there is a modern equivalent you can swap in for cheap with little or no mods.
I don't know where you live, but a competent local shop could rebuild the engine for you. A lot of places will be nervous about working on something so old, but they're actually pretty simple engines just like dirt bike engines that have been around forever.
85 Tri-Zinger 60
85 ATC250SX
86 ATC250SX
87 ATC250SX
02 XR650L conversion
84 ATC 480R