For a Big Block I would go with a well build 10 to 1 400 B Block with Edelbrock heads and Edelbrock's Pro-Flo EFI system. A big bore short stroke motor and with the right cam 500 HP and 6500 RPM isn't that hard to get. And still very street friendly. With a Keisler 5 spd over-drive, 3.55 gears and 500 HP 150+ MPH in a E Body is doable. A coilover K Frame set-up and a IRS with coilovers out back.
For a small block a 400+ CID R-3 Block with W-9 Heads and a EFI system would be cool. This would take more fab work and more $$$ too.
But for me I would dig the 3800 Lbs E Body and stick it in a 3000 lbs A Body.
