I've done as much digging as I know how and I simply cannot find any information on this frame, It has a sticker on the lower referencing a shop called "Helens Bicycles" and as far as I'm aware it was sold for bicycle tours. It has caliper brakes and an older style threaded head. I do know the Rock Shoxs are after market and I'm using the rims the bike came with which match the gear shifter etc (Shimano Deore XT light action)
As indicated on the frame, it is an SX Mt. Fuji Ltd. produced by Fuji. It was the top of the line steel MTB model for Fuji in the late 80's and early 90's. Frame is made from Tange Prestige tubing, the top of the line tubing from Tange. It is possible that the decal near the top of the seat tube is a tubing decal, which should say Tange Prestige. It's a very high quality bike.
That was a pretty nice bike, back in the day. Probably around 1987-1990. Fuji used high quality Tange steel double butted lightweight tubing for their higher end frames
It would definitely be a nice bike to rehab-renovate if there isn’t any substantial rust on-inside the frame.
I would remove the rack and install a rigid fork at the least. And maybe replace the crankset with one with a single chainring, like a white industry Eno remove the front derailleur and front shifter.