Should I remove the service valves (leaving hoses connected) and just reverse them? (put the bottom one on top and the top one on the bottom).
The top port is definitely the suction side in this picture.
+1
YEP, they are backwards. Yes, just unbolt from the compressor at that big nut. You may consider a new seal, though they are rather forgiving. If using R-12, DEFINATELY consider making sure there are no leaks first before adding the R-12. 'Stuff is liquid-gold
If you haven't replaced the expansion valve and it's been down for a while, chances are it will be bad too. Personally, I wouldn't charge it without doing it too. If you choose to charge it anyways, be sure to have a good R-12manifold set and see if your pressures are correct per your ambient temperatures. Also, it might be worth loading it with 134a first for a trial run so long as you have a recovery system to remove and go back to R-12 after you find it working satisfactory. Some might scream "contamination" I say better to do that than blow off big $$$$ on R-12 that pretty much nobody has equipment for recovery any longer.
Richard