A 904 behind a 550HP 3000lb car will last a long time.

It doesn't need a billet drum like a 727 because the smaller diameter has much less inertia, meaning it won't blow up like a 727 will.

Depending on how much RPM you're gonna run, you might want to upgrade the high gear drum release spring, but I've run them up to 7200 on a 340 duster without issue.

Basially just needs a manual valve body, 5.0 lever, good bands, clutches and steels, and a 5 clutch high gear drum (with matching machined pump). That should last a long time.

The other nice thing is that low gear sets are plentiful, and an easy swap.

You just have to be careful swapping different year hard parts around in a 904 because there are some subtle differences that can cause problems...