...New style 604's are great transmissions. Chrysler even sold the technology to GM. Though there not very forgiving when it comes to spinning one tire, they tend to brake the roll pin off in the differential pin letting it fly out of the case.
I did see an after-market solution that straps a band around the roll pin so it can't fly out from centrifugal force. I vaguely recall they fixed that on later models of the A604.
Aren't all Mopar 4 spd electronic trannys the same internally as the A604? The A606 is RWD (recall) and might be what some people put in A-bodies, though must cut the floor tunnel to fit.