The numbers I came up with are from my own real world experience. I also always run the low gear set which helps in the e.t. department. At the time my cars were running low 13s so my results will be more dramatic.
I love the 727 but why not run a baby version. My 727 in turbo car took over 1000 hp with no complaints. I dont build my own transmissions I have Pro Trans do them and the 904 is always cheaper. Go figure. So I can't really comment on why they are cheaper.
To run a 904 behind a big block I cut off the bell housing in a mill and bought a bolt on bell from JW. Dave over at Pro Trans scolded me and said the JW Ultrabell actually makes the case weaker and would have rather seen an adapter kit used. Next time I will do just that.