I put a rubber two piece in my 235. What I did was put one half of the seal in so that it stuck above/below the machined surfaces where the cap goes. Same with the other half.
Its difficult to describe but the seal to seal mating parts were staggered so that they were not in line with the seam between the cap and the block. I guess you could say the seam of the seal was at 2 o'clock and 8 o'clock. This prevents any oil from getting between the seal mating seams and leaking out thru the cap and block.
Its a small point but it was told me by a fellow who rebuilds engines in a machine shop.

1949 Chevy 1/2-Ton
"Sedgewick"
In the Gallery
1989 Caprice