727 -> 904

The linkage may not be a problem, the driveshaft will be about 1 1/2 inches to short, so you'll have to get another one (I don't think they can lengthen a drivshaft, but I have never worked in a driveshaft shop). Also, you may need to get a new flexplate as the 727 plate may be bigger. One the bright side, you should start putting down about 30 more HP to the ground with the 904 as it has less rotating mass.