landmass,
An AOD behind a small block is probably a better choice than a C4, since as joyridin' says, a C4 has a 1:1 top gear and highway driving will be a real downer due to the relatively loose converter and the rear gear. Lots of noise and rpms.
Performance Automatic, or one of the other AOD suppliers can guide you as to what type AOD to get (electronic or mechanical control) and also the stall speed of the converter which will be based on your engine specs, car weight, rear end gear, etc. The AOD has the overdrive top gear which will make highway cruising much more fun.
The AOD should survive the drag racing and road racing OK, given proper modifications for the trans and the torque converter. The keys are maximizing
oil flow, and a large
oil cooler - mine has its own big fan. Both the trans and converter must be built to provide extra
oil flow for any road racing work.
I enjoy my automatic a lot! However my 521 makes enough low speed torque that I use a 1600 rpm converter for lower heat generation and a C6 trans built by Rossler. Out back there's a 2.75 gear for tolerable highway rpms.
Take this any way you will - it took me three converters and four transmissions to learn the above lessons - the final setup has seen more than 20,000 miles and a lot of track days including places like Sebring and Daytona without any drama.
Can you tell I like it?
Tom
PS: Are you going to the DSCC touring weekend this Thursday - Sunday in Brunswick Georgia? We already have about 30 Cobras from all over to meet up with...