Ive heard of, and probably done a lot of dodgy things myself in my time, but ive never heard of anyone cutting a crank up then rewelding it. Thats pretty mental.
I dont think its actually possible, having come from CA engines which @*!# their big ends every 20 minutes I know that even a light score can cause issues, a total reweld is never going to be balanced again. I can see that perhaps the very front part where the pulley attaches might have been grafted on, but like I say, if its not thrown a shell within 5 seconds of starting its probably not so much of a bodge job as you think
I'd be amazed if you could weld and retain balance, if you could the cost would outweigh a new crank ? I would expect it take shake the engine to pieces
I think it warrants further investigation, is it possible he has got it wrong ?
Crap news mate