I would recomend the powerglide swap, even in stock form they are pretty stout units especially the ones w/ the 1.76 plantaries. If built right a glide can with stand up to 2000 Hp or more depending on internals.
Only down side would be that you'll need more gear with a glide verses a three speed. Also a glide is a much more consistent tranny for bracket racing becuase it only shifts one time.
Less variables = more consistency = winning.
Goodluck, Charles