mopars are still out in the weeds!
I had put a 72 340 in my 78 Volare. My 78 Volare had an interior fire. It sat behind the garage for about 10 years and I pulled motor/trans/rear for a future project. Upon tearing it down, I found a mouse nest in the valley pan. The only thing I can think of is that they came in thru the exhaust into the heads. I have no idea how they got into the valley pan. After the engine has been setting for several years, it sould be opened up and checked. If you don't, watch your oil pressure like a hawk that hasn't eat for a month. I still have the 72 340 and have it bored .0300 with new Ross .514 gram pistons for my 69 Dart.
What I'm trying to say is that you can't trust the critters. They will get where you don't think they can't. Can you figure out how the mice got into the lifter galley. I would love to know.