904 vs 727?

dirty white boy said

lotta folks like the 904 cause thay dont explode in the burn out box! but you ant worried bout that, a truck used as a truck can benefit from the stoughter 727,.. but that /6 alt not hurt ether!! 904 will spin up a lil quicker,.. and would be better from a mpg point of view! money wise, you got both, so buying a converter or a drive shaft is what it comes down too....its a choice only you can decide correctly on!

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Really? What's different in a 904 vs a 727 where the lighter duty trans wouldn't explode? From what i remember they're pretty similar inside except everything is just bigger within a 727.
And money wise I'm gonna need a converter either way, and I'd definitely have to go thru the 904 since it was acquired as a "good core" with history and whether it works or not is unknown.
Only thing within the 727 that's got me wondering is knowing that it is (was) a L/U version and that part isn't working though it works great otherwise.
And why that is the case, what it would take to get it working, whether it would be worth messing with to get that part of it working.
I did change the fluid in the 727 when I 1st got the truck running, had to because the pan gasket was leaking like a sieve. The old fluid was clean and red, no crap laying in the pan.