Welcome to GTOforum,
How does the 455 compare to the pontiac 400 in physical size?
The 455 is basically the same size as the 400, difference is bore, stroke, main bolts and a few other minor changes.
Can you bolt a 700R4 to either the 455 or 400?
It will work with modifications,
http://transmissioncenter.net/700R4_Swap_Info.htm
What is the best choice for headers...as far as fitment is concerned?
I am happy with my Hookers.
