If its knurled where the seal goes you are going to have a hard time sealing it with a rubber type seal. I ran into this with my 440. I put 2 rubber type seals in mine and both leaked. So I ended up getting a old school rope seal and the leak is gone. I used a Victor-Reniez from Autozone. Do a search on this issue and you will see where many have had problems sealing up their big blocks.