Ok, if you are pulling the threads out of the drum or pulling the threads off of the bolts, something is worn out beyond use. If you put the wheel on and tighten down the bolts, do they fail to hold and spin or come out? As a rule of thumb, you need to have engagement of the threads equal to the diameter of the bolt. If you are not getting that, you may just need longer bolts. Yes I know they are not cheap or free. If the threads are completely gone, corroded away, stripped out of the brake drum, you have nothing to lose. You can either try to tap the holes out to a larger size and use larger bolts (larger in diameter) to get the drum off, or you can drill out and put helicoils in the holes to use the same size as the present bolts to pull the drum. I have never heard of someone running a drum with helicoils in the bolt holes. I don't recommend it off hand. You probably need to find a new used drum when you get this one off.

Thanks Mike.

I think it's 50 / 50 between the threads out the holes and off the bolts. As I tighten the bolts down on the wheel only 2 out of 5 tighten properly enough for me to feel confident they'd hold so I do need to do some work on it.

I have a 1/2" tap so I'm going to see if I can clean the threads up and , for now, "borrow" some of the bolts off my other wheels just to try and get the drum off

Finding a "new" used drum ; there's a challenge!

I have a drum I can sell you although the shipping may be as much as the drum.