[Zeke]

You are probably going to go thru more than one bit. You could order several small bits of the same size from a quality supplier like McMaster
Carr and some just a little bigger than the weld itself (which will vary in size). Drill thru the center of the weld as a pilot and then start the bigger bit. Once thru the first body part, it should separate looking much like you used a spot weld bit. Try to buy the larger bit with a flatter point profile; some are really too steep and will go thru before the parts separate. As i understand it, the spot weld bits are spendy. You can buy alot of common bits for the same $. You'll need 'em.