One thing I can perhaps offer, although I am embarrassed to admit, is that at least on my '63 you can put the crossember under the frame rail rather than in the U section.
It does make the crossmember more visible in the side view, and it does mess with your u joint angles unfavorably - but it also allows the installation (TH400, in my case) with out a lot of savage brutality to the floor pan.
K
You can see it towards the forward edge of the door; I've been meaning to go back and redo this but have not done it yet -
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'63 LeMans Convertible
'63 Grand Prix
'65 GTO - original, unrestored, Dad was original owner, 5000 original mile Royal Pontiac factory racer
'74 Chevelle - original owner, 9.56 @ 139 mph best
http://www.superchevy.com/features/s...hevy-chevelle/
My Pontiac Story: http://forums.maxperformanceinc.com/...d.php?t=560524
"Intro from an old Assembly Plant Guy":http://67-72chevytrucks.com/vboard/s...d.php?t=342926