Check the maintenance records.

Go through the owner's manual page by page and take note of what doesn't work.

There are two or three SDLs on sfbay.craigslist.org. Check those for comparison. I can think of one Peninsula forum member with an SDL who might have some time for you to check his car for comparison. What to note = how do the seats feel, how does the steering respond, how does the car track, how does the suspension feel, how does the transmission shift, how do the engine temp and oil pressure gauges behave, what noises do you hear, etc.

If you're not in a hurry, wait for the summer when you can properly test the cooling and AC systems before buying. This is particularly true of an R134a conversion that might not be up to the task. Shouldn't be that big of a problem if you drive around the San Carlos area. You will feel a deficient AC system in San Jose. I'm not suggesting there's a relationship between engine temp and cabin temp but you can't properly test either system this time of year.

Sixto
87 300D