727 or 904?

If you have the 727, it will be a little heavier, it will take a little bit of power, but a basically stock one with a shift kit will live forever behind your stroker in an Abody with street sized/type tires. A 727 will live taking 500hp like it deals with 230.
A 904 will be lighter, will take less power to run, and will require more (a lot more by my definition) money to build to a level I would be comfortable with recommending to a customer. I'd get rid of the single wound spring and upgrade the drum as one mod. I'd upgrade the pump support. I run the Red Alto frictions in the ones I build. A deep pan too.
So as far as what I'd recommend - the 727 will run about $600 in hard parts to live forever assuming the driveshaft and rear stay intact. The 904 will run about $1300 in hard parts to be at a level I'd say "go for it" confidently. Both will work fine. Plenty of 904 guys get beat by 727s. If one thinks the transmission is what's making a car fast at the slower-than-10.50s range it's a mistaken fantasy. I'd build the 727. It's cheapest, because I'm broke and because most of my customers are very concerned with budgets.