I tried to put the heat shield on my 455 powered 69. That required removing the lower front head bolt. Well it came out with the threads smushed (that's a technical term). The block thread seems to be OK. I have the correct bolt with stud for the heat shield. It's a very little bit longer than the old bolt (probably less than 1/16" longer. ) When I installed it the threads got Smushed a bit and it didn't want to go in far enough to seat on the head casting. I'm afraid to push this bolt any more to torque it. I've tried the obvious and put a screw driver into the hole. I've got at least 1/4 " of extra room before the bolt bottoms out. I think a flat washers under the bolt head should do the trick. But I'm not sure I can properly torque it with a washer there. I think I can but I'd like another opinion. Should I recut the "smushed" bolt threads before I install it?
Any help is appreciated.

Yep. Run the bolt through a die and even better re-tap the hole to be safe.

Use thread chasers instead of taps and dies. Taps and dies are made for cutting threads. Chasers are for repairing existing threads. I got a set from Sears years ago and use them frequently for cleaning up holes and bolts.

X

X2. I have a set I use all the time, very cheap.

X3
I have a thread chaser steel file. I has 8 thread pattern options.

I would replace the head bolt myself.