TPS bolts broken.

[1979C20]

My buddy has a 90 c1500 and he went to change his bad TPS and the heads of both bolts snapped off. He had a spare throttle body base laying around and just swapped it. He gave me his old one(with broken bolts) so I can do the Ultimate TBI mod to it without my truck being down. My question is, how can I get the bolts out? Theyre aluminum bolts, I ran a drill through one and pounded an allen key into the hole in the bolt and it just rounded the hole out when I attempted to turn the allen key. Its hard to tell where the bolt ends and the throttle body begins. I dont think an extractor will work. Any ideas?

[Irish_Alley]

well you need to see how long the stock bolts are, and go from there. but why did you pound a allen key onto it?

[VileZambonie]

Drill them straight and use either an insert or go oversize

[1979C20]

Since they are aluminum bolts I figured if I drilled a hole in the middle and pounded an allen key in, the hole would take the shape of the allen and act as if it were an allen head bolt. Does anybody know the original size of the bolts?