Hi spec,
My preferred method would be sifbronze but you would need to find someone with oxy acetylene welding equipment. For the best joint I would grind a champher on both edges until they almost met in a point. For your job I would only grind the underside so the join was not so visible from the top. Many years ago I had to repair the flange on the starter motor of my sisters then boyfriend's (Now husband) Jag. I first repaired one side. (Two bolt hole fixing) Then later the other side broke and I repaired that side as well. The car also had starting problems at the time. I traced the fault to the centrifugal advance mechanism in the distributer. It was stuck in the fully advanced position. On both occasions the starter flange had broken after trying to start the car when the battery was low. The problem was under those conditions when the engine turned over slowly it fired long before TDC and the engine then tried to turn the starter backwards. The sifbronze joints survived better than the original cast iron. I have heard that you can get welding rods for welding cast iron with an normal stick arc welder but I have never tried them. It may be possible to use sifbronze with your TIG welder but the fumes from the flux may contaminate the tungsten tip. I did an internet search for "sifbronze TIG" and found
this page so it looks like it would be possible.
Edit, I've just seen Eric's post so it looks like that could be another solution. (I think you would have to use the pure argon from your TIG welder with the stainless steel wire on your MIG.)
Les.