with the longer stroke crank in there plus rods so far out you got to notch hell out of the block shirk, rods going lots lower into pan /oil level you creat a lots more windage that foams/whips the oil into a mist


also on some of those longer stroke cranks, I've seen the rod oiling holes so far off location that the flow misses the rods-----also maybe excessive rod side clearance which would not only give a drop in pressure but add to the windage --------


also those longer stroke cranks require a smaller base circle cam which(as Pat said) can let the lifter groove come below the tappet hole-----do you have restrictors in the lifter galleys??