[Bob Carriere]

My best guess Phil is that on a 261 the oil comes out of the lower left hand side hole directly from a passage from the oil pump.... up through the filter and back into the oil galley on the upper ridge right hand side.....

Now on a by-pass system of the 235 it comes out of the right hand side pressurized oil galley....volume controlled by line size... to the by pass filter out of the filter to the bottom left hand side hole that drains into the block.

Upon careful examination of your pictures there are some differences in the ridges hidding the oil galleys ... smaller on the 235 and larger on the 261.

STEW.... wake up.. we need pictures of your "puny" little holes in your 261... origin unknown.....

I am convinced the block I have been shopping for is a 261... has Captians bar above starter.... casting block number matches the 58-62 sequence in GM records... and serial number tells it is Windsor made...... need to read the casting date for month year...

Meanwhile here is another shot of my engine showing the dual spin-on filters.....