I wonder with the cheap price and plethora of late R200 short nosed diffs and CVs if
there is someone who has a kit/frame to suit retrofitting into earlier 1600 510 chassis?!
The main problem is that a long nosed diff forms a structural part of the whole rear x-member assembly. Short nosed don't (and can't) due to only having one set of mounting bolts at the front.
You need to build the structure into the x-member so that the x-member is "rigid" all the way from the outside mounting points through to the moustache bar mounts rather than using the diff to make it "rigid"
Not impossible, but I guess its a question of whether a new x-member can be built at a reasonable cost.