I haven’t used the search function here for a while, but there are several old threads using 3/4” plywood cutouts and a press or other means of force. I would lubricate the old bead area with Gibbs penetrant. You’ll get it.
We weld shaped 1/4” plate to our Sears Runabout cast aluminum scrub brake plate with our Millermatic 141 aluminum spool gun and shielding gas. Works pretty good till OMB gets their inventory back-order. All I got.
I googled for images of our H35 throttle-governor control and found a few good closeups. Yours should be danger close to the same. Gotta pull the shroud. Didn’t even have to open the L head manual.
You can read about pipe threads, modify an inexpensive pipe tap by cutting off the first several taper threads, and tap the hole a bit bigger. Then cut the first several threads off the male NPT to fit well. NPT are tapered, move the poorly-fitting taper further up the taper diameter. Hope...