Heli Coil

Anyone used Heli Coils for repairing this type of problem? Have tried extractors, left threaded drills, they will not budge.

Your advice has been wonderful so don't stop now. Thanks.

If you’re gonna remove the busted bolts by drilling them out, you can simply drill and tap the holes for the next larger screw size. Then drill out the mating frame rail holes to accept the larger diameter and install oversize cap screws. This would be cheapest.

Or you can drill out the holes, tap ‘em for helicoil’s and install new capscrews same size as the originals. But you’ll need to buy a special helicoil tap and a helicoil insertion tool in addition to the helicoil “springs” themselves. (FWIW properly installed helicoils are more difficult to strip out than the original tapped theads. I've used 'em and they work great)

However before going to all that trouble you might engage the services of a good welder. By welding a large nub on the end of the bolt, then grabbing it with a vicegrips, very often the stuck bolt will twist right out. (The extreme heating that occurs during welding does wonders to break impossibly stuck threads). I’ve had excellent luck over the years with this method.

Good luck!