We just started restoring an 87. The shocks will need to be replaced. What are my options? Is the rear rebuildable?

Rear is rebuildable and actually the stock rear is a decent shock
As for fronts ,works,elka ,even peps will make a shock for you.
Cheap option is a 04-08 (carb model) yam 450 front shocks.
Some small amount of grinding is needed for fitment

Yep I'm running YFZ450 fronts,a bit stiff for MX with stock length control arms on mine but for general riding they work fine.You could have them revalved and resprung though as they are rebuildable.....I had the top of the shock milled off even to be sure the shock was centered.