Sounds like a fun project! I had an '85(?) Cimarron at one point, too. I ended up putting drop bars and barcons on it, and selling it locally as a city commuter.
Before that, I had it set up as "Poor Man's Rivendell":
It was a little too big for me, and I ended up with a wonderful mid-80's Trek MTB in a slightly smaller size.
I think without a robust parts bin, going "period correct" will end up getting more expensive than you think, unless you have access to a co-op (an open one, at that), or like you say, find a similar intact MTB and swap over parts. In the end, you might be dissatisfied with what you get for all that effort.
Personally, I would just pick and choose the parts that I like, have experience with, or want to try out. The nice thing about old MTBs like this is that they're great platforms for experimenting with different riding styles (trail, upright, drop bars).
Looking forward to seeing how you decide to build it up! I broke my foot 2 weeks ago and unfortunately won't be riding ANYTHING until mid-June at the earliest, so I'm living vicariously until then.