I don`t know about the weldability of diferent aluminums- sometimes we do aluminum repairs at work and we just kind of cross our fingers and stick it together, so as you can guess we talke a pretty "Flintstone" approach that wouldn`t cut it for critical applications like that. Still, with the hollow s in the "good stuff", I don`t think you`d find somebody who knew what he was doing to accept that job for less than what you`d pay for custom arms.

I didn`t know there were cromo arms out there. If anything, I`d guess the best chance for "stretching" would be that route.

Machining a set from scratch wouldn`t be any easy affair either and I still doubt you`d end up with hollow arms or fancy BBs. Drilling and tapping the pedal hole is the least of the problems- you`d almost have to buy a custom broach for the taper interface, which you by itself would run a lot more than the $450 - $600 you`re looking at from Zinn or wherever. For Isis or Hollowtech, it would be a fortune- the only advantage you`d see is getting the BCD you wanted.