Barry,
There are countless methods obviously and so many highly experienced builders/ Pilots on the forum will surely have there full proof tricks that work great, to add to the many great ideas, I have personally drilled the threads out of my engine blocks and ran longer bolts (using the thin layer of orange high temp permatex gaskets) with a lock washer and nut,"provided the pipe is threaded" I tighten it up and put a couple of Heat Cycles on the motor/pipe and re-torque. And I haven't had one back out yet.. Good luck dude!!
K