First be sure that you use the ultra hot coating as the normal stuff will not take the exhaust temps that we generate in many cases.
Then it becomes a question of how much do you wish to spend.
You can put a gusset between three and five to bridge the gap above the weld. You can weld around each tube at the flange and then port the inside for a better match to the head.
I am not sure that siimply welding over the existing weld is a good idea....maybe a real welder can answer that one.