"my question is what should I do so the trans/rear end won't blow up the first time I floor it?"

The biggest problem I've had with my 74 Charger (440 with 420hp/510flb) was the rear suspension. There's more rubber in the oval shaped leaf spring mounts of the 73-74 Chargers. The rear suspension lets the axel wrap up and breaks things like u-joints, drive shafts and pinion yokes. I plan to change over to 71-72 type leaf springs and possibly a set of Cal-tracks.

A stroker 440 would be very cool, but if you only want 400-500hp, you might find it a unnecessary expense.