Does T/A, or somebody, sell BBB manifold end seals?

To answer your question on the end seals, yes TA does sell them for the 455. TA1239B $8.90 for the pair.
Also stock them for the;
198, 215 V8 / Rover, 225, 231, 300, 340, 350, 400, 430, 455

 

I had the bulldog heads on my old 464 and it required a bead of silicone on both the front and back lips - I think it was easily a 1/4" thick, maybe 3/8" - used the black permaseal stuff in a the pressurized can - never had any issues.