I think there are probably better (easier) ways to make the 69 handle well than all the chopping you are considering. Cage the 69, aluminum body mounts, Del-a-lum or other bushing in the arms, do the Guldstrand mod for the UCAs, get a better alignment (as Guldstrand recommends), put a IROC quick ratio steering box in it, etc, some good sway bars from your favorite source.
Check out David Pozzi's website for lots of great information on First Gen suspension, brakes, etc. pozziracing.com I think is the addy. Good luck, and don't give up!
A twin turbo LS1 would be sweet in the 69
