Yes I can confirm the straight shaft pots won't be any use so into the spares box for a future project they go.
I squeezed the split shaft together on one of the pots I had with a small metal clamp and in the process dropped it on a tiled floor breaking off a terminal. Nevertheless this game me something to go to town on as practice and I now think I can get it on low enough with a tight fit. I tried it through the selector hole rather than ream out the volume/tone holes in the scratchplate and with a bit of packing out it should be OK.
Just a quick general question though, apart from copper tape on the back side of the scratchplate, should there be any insulation between the pots and their locking nut and washer and the tape? Also why do they have a small protruding rod at 90 degrees to the plate? (As photo).