Yes, it is indeed a 340... I have had timing jump advanced during cranking from a loose distributor, it could have contributed to blowing a head gasket. Being it is a rare and expensive to replace (impossible to replace if it is a matching numbers block!) 340, I would plan on pulling the engine to at a minimum pressure test, magnaflux, hone the pitting out of cylinders and re-ring (if it doesn't open piston to ring up excessively), and making sure coolant oil mix hasn't started corroding or spalling the bearings. Even if it means having to save up to do it, drain the crank case before putting it in storage, overfill crank case with fresh lube, cosmoline spray the crap out of the exposed cylinder walls and heads. If you need to, score a boneyard 318 or 360 if you want to drive it while waiting to refresh current engine. You could even use your cylinder heads, intake,cam, etc. in it if they check out okay. It's just not worth the risk of irreparably damaging a 340 (especially if it's numbers matching) block with a bearing failure or gouging out a cylinder wall with a broken ring...
