drilling out the u joint and welding would be my suggestion.
few things to keep in mind are:
- strength,
if this fails, it might not turn out too good. (i'm not a fan of welding the socket to the shaft then just snapping the u joint into the socket, could come off too easily, unlikely yes, but i still don't like it.)
- play, make sure there is very little to (preferably) no play in the system.
- consider that you may wish to disassemble the parts at some point, if everything is welded in place you will have to cut some stuff off.
- also consider how the u joint may wear in a dusty or dirty environment, most u-joints have rubber boots to prevent debris getting stuck in the u joint causing excessive wear.
maybe this would be a better choice, you can till use the socket u-joint, but if you have a little bit of money it may be worth your while.
https://www.surpluscenter.com/item.asp?item=1-2738&catname=powerTrans