We used to weld and straighten OHC Aluminum heads all the time. As someone else mentioned it needs to be super clean and heated in an oven. Good machine shops can do this without it costing an arm and a leg (i think we only charged 35-50 bucks for the welding, but then there was charges for installing new valve seats. We didn't really charge for removing the old seats as we would just cut them at the crack, then grind a v-groove in the crack anyway). We used an aluminum welder guy that made custom tanks and bottles (industrial stuff), he never welded automotive stuff until we approached him but he was good (and cheap...he'd see these little 1 inch welds and say $10 or $20). To straighten them we heated in an oven then we would set them up in a press and "bend" them the other way (we did a lot of measuring and setup but essentially just bent them the other way).

The crack he has may not have cracked all the way through yet, thus no indication from oil fouling or exhaust steam.