273 Exh Port MisMatch

Since the other 3 ports on that same head are in the proper position it looks like the one port had a misplaced or broken exhaust port core when that cylinder head was cast in the foundry.
I would look for a replacement head.
If you choose to repair the existing head, to properly weld gray iron the entire head should be preheated to around 1100 F prevent cracking. And then you can get into some warping when heating a fully machined casting.
If you really need to save that head building up the gasket area with some kind of high temp epoxy may work for a while.
Another option would be to see if Remflex has a gasket that fits a 273. The Remflex gaskets are thick and are much more robust against blowing out than a stock style gasket. Perhaps a combination of a Remflex gasket with a healthy glob of high temp epoxy as filler for the missing material around the outside would make a long lasting seal.