oil tank and battery box

Can one install a 1971 and up commando oil tank and battery tray/box in a 1970 commando frame and use the 1970 side covers?

Fitting the oil tank and battery carrier shouldn't be much of a problem, however (as I assume you are talking about a Roadster) the right-hand 1970 cover is the battery access panel and the left-hand is the fixed panel with the ignition switch, whereas the 1971 and later right-hand panel is fixed (screwed to the oil tank) and the left-hand panel is the battery access so you would have to modify the 1970 panel for left hand battery access and fix the right-hand panel which wouldn't mount to the 1971 oil tank in the same way as the panel shapes are different although it may be possible to use the original right-hand panel mountings, I'm not sure.