Whether or not the lock-up converter had anything to do with the failure, it was never intended to be used in performance applications. Valve bodies are different too and the parts don't interchange, but I don't know what the differences are. With the right parts, a lock-up trans can be converterted to a non-lock-up and, of course, the low gear sets do interchange. A regular 904 trans, built properly, will work fine. But a regular 727 is stronger and will likely last longer simply because of the bigger, stronger parts used. The key words are "regular" and "non lock-up". I have a few years on the 904 in my car built by JW but may swap it out for freshening this off-season to be safe. Nothing special or trick, just their reverse manual valve body, a low gear set and whatever HD bands and clutches they use. I also use Amsoil Supershift synthetic fluid.

I have heard that OEM bands may not hold up to hard shifts because of the material. Same reasoning if using a 5.0 lever. There are a couple different performance bands too. Between "blue" and "red", I believe the red are best. I just never got into transmissions and let JW take care of that.

I don't think a freewheeling low gear is a good idea on the street either.