Tristan Kulow

I was installing my new manifold when one of the bolts broke off half way through. I did the standard drill the bolt out and attempt to retap the hole. Well i drilled to low and had to weld the hole shut so I could redrill the correct position of the hole. I can't for some reason get the bit to catch almost tempted to resort to a diamond tipped bit to see if that would go through. Also the hole was stick welded shut.What should i do to redrill and retap this hole?

TieRod the manifold I have is an edelbrock C427, its an old one but it was recently restored to almost new condition.

I bought a new manifold and it didn't come with these adapters, the old ones won't come off so i need to but new ones.