Hi Jim,
I'm taking a guess at this. On my 235 the back left side of the block is were my oil pressure switch goes. It is "tee'd" (3 way fitting)in with the bottom oil return line, from the oil canister.
And the timing mark on mine is a triangle for TDC I believe. Each of those lines is 5 degrees.I forget what the circle is. I hope this helps.
Chevyboy62
