I think you'll find this is a question about transfer boxes rather than gearboxes Michael.
Yes it should fit. I have fitted a 100 series gearbox to an 80 4.2 24v manual. No issues at all with refitting the original 80 transfer box with regard to props, bolts to the gearbox, electrical, breathers etc. It will be a different part number I think because from memory it might have has some extra stiffeners or ribs in the casting.
So in summary - if a 100 gearbox will fit, then so will the 100 series transfer box. The key difference might be in the internals of the transfer box itself with regard to ratios etc. I can't tell you that. Also not sure if the 100 had the same viscous coupling as the 80. (Some models of 80 didn't have that either) Make sure you measure the length of yours from flange to flange is the same as the 100 series or you'll need a different length prop!