The EFI part is pretty dependable as long as you have a good battery... the 580 engine is not known for it's long-term reliability, especially if they don't get regular maintenance.
ZR's corner GREAT and the 580 makes a ton of power, both in carb version and in EFI.
A/C of that era also have issues with the PTO side driveshaft bearing, if the sled has high miles and has not had the bearings replaced on the driveshaft and jackshaft, that may be something you want to get done...
Mine both came with Fox shocks which are rebuildable and when they are fresh, they work pretty well.
I am currently reconditioning a 94 zr580 with a 95efi motor this is my first cat and hoping for the best. I do have the original motor which needs a sleeve and rod work. Anyone have any interest in it?