Ron, A quick check of a 1929-46 Chevy Master Parts book shows the 1936 FB rear axle listed as GM# 601925. A one year only axle per my research. It doesn't cross over to any other axle housing that I could find. Doesn't necessarily mean a Task Force open drive differential (third member) won't bolt in, but I would say not likely.
A little snooping through some older threads in Stovebolt came across this
conversation much like yours. The last reply by Bolter Pre '68 Dave suggest using a later 1947-50 1/2ton axle mated with the Task force differential to get what you seek.
I saw the 33-63 carrier and cover gaskets are all the same, so it seems the third member will at least bolt in. Question now would be would my axles work?(diameter, spline count, location etc)
Two other issues come to mind (just thinking out loud here)...Could I upgrade the rear brakes to Bendix style on this housing? On the front axles, I think it would just be a matter of drilling the 7/16 holes to 1/2", but I don't know if the rear would also be the same.
Also, availability of new bearings.
