Dear Rob;
I'm not sure what the "best" seal is etc.
The method I described is how It's done on all inline Chevy 6 engines from 37-62. GMC is the same basic 'rope' seal as they are.
The "trim" is easly done on the cap with a single edge razor blade. The block side is recessed (after the crush).
This method is as close to 'foolproof' as it gets. The only time it doesn't work well is with a new seal on the cap and an old (stiff/hard) seal in the block with an old loose bearing.
Pic #3 is the seal sticking out of the block??
