You can buy the"O"ring kit to fix the oil filter adapt. Its only a few bucks.
If you do a reverse flush be careful of the heater hose connections, they are old and fragile.
On my 90' I just added the flush to coolant bottle ("turtle") and followed the directions. Drained, flushed til water ran clear, drained again, you want to get out all the tap water that you can, it will leave mineral deposits in the cooling system, so use distilled water when replacing the coolant or buy 50/50 mix. I used the mix last time and had no probs. with freezing, gets to well below zero here (-10/-15 is not uncommon).
Don't forget to replace your thermostat and check you hoses.