Need info on rear axle from 48 business coupe.

Jeff, the carrier from '48 and later won't fit in the '36 housing, so you'll have to swap the entire assembly. I think you'll find the tread dimension just right, or only an inch or so too narrow, which you can fix with a 1/2" spacer on each side. I did a stepdown rear axle into a '38T in the olden days, and found it just 2" too narrow. Worked that with offset rims. But the '36 tread is narrower than '38, so it should be very close. Not too difficult, just reposition the spring perches, being careful to get the vertical angle of the pinion shaft the same as the transmission tailshaft (i.e., the two should be parallel). You'll probably want to find a 3.58 ratio carrier assy from a '51 with Hydramatic to replace the one that's in there now. Or, if you want a wider range of gear ratios, forget the '48-'51 axle and put in a Dana unit from a '52-'54. Job is the same as for the '48-'51 axle.

'36 u-joints are first with U-bolts holding the joint to the flanges, and are same as all later ones. Jet rear axle would be too narrow for '36, and brakes would also be rather innefective compared to the Bendix on the '36. Probably wheel bolt pattern would be the same.

Jeff, all things considered, I think you'd be best off putting a '52-'54 Hudson (Dana/Spicer) axle assy under that car. Keeping it all Hudson makes life simpler when it comes to replacing brake shoes, wheel cylinders, etc., as you can get it all while staying in the Hudson parts resources community. By going with the Dana vs. earlier stepdown axle, you eliminate the "unobtainable wheel bearing" problem the earlier axles have. And there's a wide range of gear ratios available for the Dana, in case you're not happy with whatever you try first.