Maybe sell the heads to someone who could use them "as is" and get another set done properly if the math works out anywhere close, I mean if you can sell them for $3000 and buy replacements with the proper thickness for $4000 then it only cost $1000 to "fix" them the best possible way VS what your talking about, and don't forget welding them like that will mess with the valve seats and they should be reground at minimum but they will loosen up and shift during the process and really should be replaced.

I love yankee engineering my stuff but I think this is a bad idea on $4000 heads