Any of the modern oils will be better than what was available when new. I use 10W40 in the winter and 20W50 in the summer. You will get differing opinions on this, but I have driven long distances and 8000+ miles in my `31 with no problems.
You can usually get by with a brass float and a gross-jet in the carburator. Gaskets are minimal and can be fabricated. Kits are available though. As for the transmission and the rear. Todays 90W is OK. I tried the mineral oil for a while, but it caused shifting problem on long trips. I went back to the modern stuff.