Just pulled my /6......Now I need some answers

there are 904's in the 9's...

but stock vs stock the 727 is stronger...

And there are 7 sec powerglides , still prefer a 727 0ver a 904 . 904 needs a serious rebuild to stand up to a good 360 , the 727 will do it stock . I have yet to blow a 727 , had one in a 650 HP 440 that took a beating for over 150,000 miles , my 1971 340 clone lasted over 90,000 miles and 6 years with 727 , 10,000 miles and went through 4 904 with coolers and shift kits .
904 might be better these days ,but it is not as strong as a 727 without major improvements
For blasts up the track the weight savings of 904 might pay off , for a a street car that is driven often the 727 is a better stronger choice , I M O .
Which transmission is easier to find these days ?

And change the dif for sure ! Those 7 1/4 are weak , the torque of your 360 will have it spitting teeth , went through many of those before I wised up and put in an 8 3/4 . 8 1/4 might be good enough , depending on what is available , no experience with 8 1/4 . I know the 8 3/4 is a super tough , easy to change gears dif .
Good luck !