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screw a short stud into the hole and tack weld it..

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but I'll go further.

Use an allen-head setscrew and put it in with blue locktite or maybe some epoxy. Spin the converter 360° to ensure the setscrew doesn't hit the block. Then put a locknut on it - make sure locknut is below the surface of the setscrew and/or spin it again.

Use an allen-head so that you can positively hold the setscrew whilst tightening the nut and thereby avoid jumping the threads. Should probably use a distorted-thread locknut as those have a smaller profile than a nylon-insert nut.