As Bill stated you could expand it slightly.
Blue (med stregnth) locktite or locktite pipe sealant w/ teflon (like the tape only liquid in a tube) will give an tight seal to the block.


BC
1960 Chevy C10 driver 261 T5 4.10 dana 44 power loc
1949 GMC 250 project in waiting
1960 C60 pasture art
Retired GM dealer tech. 1980 - 2022