I have a set of 3/8" straight pipe dies just for playing with the pick up.Curious. How did you get to this point? Post a pic of the end of the pickup and a pic of it “to far” into the block.
The factory PU is a straight thread. The tube is soft and likely the cause of any slop. If the first couple threads of the PU look rolled, that likely the problem. Seems unlikely the block threads gave-it-up unless something went really wrong.
I’d also guess that a little PU thread clean up, and chase it with a die you could’ve simply get it tight with one more PU rotation.
not terrible idea , but if I were going to drill it and tapp it for 1/2'' , I`d sure buy a 1/2'' pick up and put in it .You can always tap it to 1/2", then use a 1/2"x3/8" bush to put your original pickup back in. IIWM, i'd use a harder set threadlock on the 1/2" threads.