A large socket rolled over the seal works pretty good. Heres how I assemble Pontiac's, they use a two piece rope seal, I install the one piece of the seal in the block leaving it long, drop in the crank, and use a block of wood to tap the crank down into the seal till the crank hits the bearing. I then remove the crank, pull the seal, install the second piece and repeat. The first piece is installed in the cap and trimmed to length. The second piece is then trimmed, and ready to use. The real key to rope seals is using
https://bestgasket.com/rear-main-seals/ brand seals if available for the engine. They are a far better seal then what comes in gasket kits.
