It's an easy swap in that no modifications are required but it does of course call for quite a lot of dismantling.
The main reason for doing it is that the Mk111 battery is partially retained by the black air filter box and few of us regard that as pleasing to the eye. If the box is simply removed then the battery will have the tendency to fall forwards. This can be countered by welding a plate on to the lip which holds the rubber battery mat.
Having done away with the air filter box, we now have to find a way of fixing the top sidecover mount. One option is to make up a bracket to fit to the Mk111 panel but if using an early side panel with built-in tool compartment (certainly in the case of the Roadster), it will foul the battery. Incidentally, that panel with tool compartment probably accounts for the scarcity of Commandos with original tool kits
If one decides to fit a pre-black box air filter (750 type) then the folded lip on the front edge of the later battery tray with the two captive nuts is slightly further back (IIRC) than the earlier type. Not insurmountable but all in all, the quickest and neatest way is to use an early tray.