904 behind a 5.9 magnum engine

I'm getting ready to put a 5.9 in my 67 Barracuda and I have 2 trannies, a 904 and a 727. I just put an 8 3/4 rear in and just had the shaft cut down so I was thinking of running the 904 to avoid having it cut down again. Every trans shop I go to says the same thing, that the 904 won't live long behing the 5.9, too much torque. I explain that the one I put behing my la 360 lived forever but they say the 5.9 makes a lot more torque than the la 360. From all I've read on here lots of people running the 904 with quite a bit of motor and its doing fine. Can anyone give me some good input/advice on this subject? Thanks, Clay