7.25 axle splines

the current setup is at 4.5 inches on my Dart. In Germany I can't get a suitable differential basket for the 7.25 rear axle. My brother currently lives near Washington DC but can't find anything suitable either. I found a 7.25 rear axle in my area but with the 4 inch bolt circle. Normally I could take the differential cage out of this rear axle and install it in mine. Then add a new planetary gear and everything should be fine, right?