Welding should only be your last resort. A mechanical fit will be more than strong enough, and will most likely end up being more accurate.
While I agree with this, even if you were to machine the cup, how is the sprocket supposed to stay where you want it to?
I don't see a grub screw on it. (the sprocket)
I understand what you mean when you said
the sprocket can slide over and lock onto the drive cup through the top of the grub screw slotting in underneath the flat spot of the sprocket bore. ,
but I don't see how this will keep the sprocket from moving sideways.
Personally I'd weld it.
Actually I'd have it machined and weld it.
If you go overkill at least you know it ain't gonna break.
Unless you wanna keep all the bits non welded in case you wanna use them for something else down the track or if it's the only one of its kind.
This is why I'm spending a bit of money and getting sprockets from a supplier who can get me more should I need them.
