if it is a short trip thats probably fine but maybe you wanna put a nut on the bolt first, screw the bolt in till it gets tight and then tighten the nut down to keep it in place. an o ring, then a washer, then the nut next to the block would be an idea as well. just so you don't screw up the threads in the block by tightening the bolt down to keep it in place.
I doubt if GM installed a regular thread into the block in an oil gallery because regular threads are not made to seal like a pipe thread or an o-ring backed thread would. since I have never seen a oring style fitting in a GM oil gallery before, on an old engine, I would say either that hole was "repaired" previously or it is a pipe thread. pipe threads are a tapered thread so the more the fitting is turned the tighter the fitting is in the hole. maybe just get'er done with the bolt for now but plan on looking into a little further when you get the truck back. I assume you are taking it to a shop for some repair so, if thats the case, make sure to tell them to keep an eye on that fitting plug so it doesn't come undone and they don't realize it. that could spell disaster in a short time.
here is a little blurb on fine thread fittings vs pipe thread fittings.
https://hydraxio.com/unf-vs-npt/