With your wealth of knowledge, I'm truly surprised about you not knowing about scrapers, aka windage trays. They sit just below the crankshaft. It's a perforated piece of sheet metal to prevent the whipped up froth of oil at high RPM from causing oil starvation to the oil pump. I believe all 340's came with one from the factory. My 1970 Swinger 340 has the factory part. Not trying to belittle you, but I can send you pics or more information, as can smarter members on my favorite site.