When it comes to the fork, one thing to consider is the frame geometry. I don't know what came on a Zaskar originally for a fork, but if your new one has a lot more travel it will affect the handling of the bike and how it feels. Generally speaking bikes from that era were either relatively short travel (50-63mm) and you will not want to go much beyond 80mm travel with a newer fork.
For chain and chainset compatibility, generally speaking newer shimano parts will work with older, but older will not always work with newer.
I'd rather see a bike back out on the trail than worry about it being correct. Go ride!
Current Stable: ///84 Ritchey Timberwolf///86 Ritchey Timber Comp///86 Ritchey Ascent///88 Cannondale SM700///89 Teesdale Quintana Roo Superform///89 Santana Moda///90 Monster Fat///90 Fisher Pargon 650b///92 Santana Moda///1997 Ted Wojcik Sof-Trac FS