You 1st task will be deciding if it sounds fine as is or not. Listen to it a few times. Is the sound appropraite for what it is (sometimes old tape noise has its own pluses) or does it need something?
Make copies and work on the copies.
Big issues for you. I hope there's some tape lead in on the digital tracks so you can take a tape noise fingerprint to deal with that issue.
You'd actually be better off getting the tapes & the machine with them & doing your own conversion to digital & then processing for noise, any hum etc. followed by trying to "spruce up" the recorded stuff.
that's going to depend on what you get though.
You might need to EQ or MBComp, enhance (a maximizer), limit, a combination of 1 or 2, all of them, which sequence etc etc etc etc etc.
I recently "spruced up" some mid 70's mono tracks from a reel machine for someone.
I worked with wave files - recorded into waverepair, dealt with the noise in waverepair too. The tracks then sounded ok but they were quiet and no bottom end.
I imported the cleaner tracks into Cakewalk proaudio to use the VSTs.
To deal with the request I used the MDA Stereo plug to get a little bit of stereo image.
There was a lack of bottom end (NOT due to denoising but the source material) so (after trying about 20 different plugs) I used a little of the sonicmaximiser plug (naughty but it does have uses - needs to be done subtly),
a little bit of EQ tweaking post max &
I used the Classic Limiter plug to listen to what would come out & that sounded OK.
All in all it came out pretty well - I liked it in mono so did a run of each.
Best quality going in means you'll have a better shot so get the reels & player if you can.
Good luck