If you don't want to pull the heads then you can modify the intake itself, first grind it flat for the bolt head to seat flat and so you can drill the holes vertical in a drill press or something, then mark them and drill them, go slowly because the drill bit will be wanting to jump around and all sorts of stuff as you go thru the original bolt hole. When you put the bolts in put some sealer on the threads and it will be ok. It does not look pretty when done but it can be done. I suppose if you wanted to fill the original bolt holes in the manifold with JB weld and sand them all down you could make it look pretty but I am not good at making stuff look good, just run good on a shoestring budget.