What should I do with my 340 that has been sitting for years.

If it ends up you have troubles, get it on a stand (with a drip tray underneath) and start soaking those cylinders/pistons. Let it sit for a few days or longer (since it sounds like you're in no rush), pivot it so you can soak it again from the top but so it can have a chance to penetrate the other side of the hole. Then, you could rotate it and do the same from the bottom if need be. Everyone has their own penetrator they like to use. (Note: Feel free folks to insert (pun #2) any joke you like here). I only use Kroil.