I put 240Z drums on my old racecar. I bought two used drums. Three things need to be done:
1. Enlarge the center hole.
2. Enlarge the lug holes.
3. Cut the lip around the circumference away. you actually have to "indent" the aluminum between the steel liner and fins to clear the lip on the backing plate.
I found that paying a machinist to do all this was more expensive than buying a pre-machined set of drums, so I bought a set already modified. I got them from a big online parts supplier whose name I forget. I gave the receipt to the new owner, so I can't look at it. You can probably Google it. You have to search the parts inventory for TR6, not TR3, because they don't list TR3.
They fit fine and looked cool.