The only welding that I have had done to a crank has been under water. I have a BMS crank in service that has has a fillet ground down from the way it was machined. It is a crank that doesn’t have rolled fillets like the stock crank. So far it hasn’t shown any adverse signs, 9+ years strong. I sent it off to one of the best crank shops in my area . It was magged and they said it would not be beneficial on that particular crank. It was a raw forging to begin with and I guess they got the width between that journal a little thin, nearly identical to yours. Before you weld it and create a potential short block issue , I would send it off to the best crank shop ( if they are familiar with Buick V6 cranks , even better) and get an opinion on it. You could make it brittle in that spot and harmonics would scatter it at high rpms. I have seen this only on cast cranks never on billets. I knew a guy so deep into cranks that he would check its resonance frequency with a tuning fork.