okay so on my '69 everything is running great. the only thing I have a problem with is the tranny. while it is very strong and reliable, i just can't live with the gas mileage the 3 speed puts out. Has anyone ever stuck a overdrive 700R4 or 4L80 behind a big block caddy? I plan to beef up my engine to make it kick out 400+ hp in the future so i'm looking for a transmission that can handle that kind of torque. which tranny would be a good choice? and how hard is it to find an adapter plate?

I've seen V-6 bellhousing 700-R's to the Northstar engine, I think you would have an expensive change over to add a 4L80E. Just the computer alone is well over a grand to operate the tranny.

Have you considered a Gear Vendors overdrive unit? They're not the most practical thing in the world, but...