Long story but my local engine shop who rebuilt my 454 neglected to check the snout of my crank and when I went to install the harmonic balancer, there were no threads in the crank. I shined a flashlight in there and there are little to nothing left.

Can someone with experience in this area tell me what I should do.

The hole oem is 1/2-20. Would you suggest a threaded insert heli-coil, or tap to a 9/16-18.

thanks for any help
jeff