Others will elaborate, correct me, and fill in the blanks.
Our '72 had a 1300. I think the 1300 ran from '67-'74. The 1500 would have started after that and run through the end of production.
You can interchange a bunch of things between the 1300 and 1500. The earlier engines were different from the 1300 and 1500.
You can mount a 1500 where a 1300 was and the other direction. However, there are differences in the gearboxes and clutches. For example, if you want to run a single rail gearbox on a 1300 you have to change the flywheel and make spacer sleeves to mount the later flywheel on the 1300 crank. I suppose you could put a 1300 clutch assembly on a 1500 but other components would have to change as well. In such swaps you are also likely to need to change the driveshafts.
Some may tell you the flywheel swaps are not required when mixing the different engines and gearboxes. When I looked into this I could not find a clutch friction disk that would allow a simple swap. No one could direct me to a source for these clutch parts.
With care and thought you can make almost all the possible 1300/1500 swaps possible.