OK, its question time. Is the 727 a standard length? Dodge made shorter 727s for some trucks and vans. Do you have the 904 handy?

You need to measure the length of both transmissions from the block surface of the bell to the rear seal mounting lip and compare the measurements. I thought a standard 727 was 3" longer then the standard 904.

Whatever the difference is, you need a driveshaft that much longer then the one you have, u-joint center to u-joint center, with the 904 front yoke.

Mopar made a lot of different combinations of trans/rear end/wheel base differences, so there are a lot of driveshaft lengths to choose from. I suspect there were several cars/truck combinations with the driveshaft length you need.

There are very few yards with a lot of old Mopars laying in them, but may still have a pile of driveshafts laying around. It might be much easier to locate av particular driveshaft length then a drive shaft from a particular car, truck, wheelbase, trans & rear end combo. At least it would be here. I have my own driveshaft collection, all I can tell you is they came out of Mopars, a length and u-joint size I can measure. Gene