A caution on aluminum pipe plugs. Unless they are anodized, they will gall and seize when used against non anodized aluminum parts. I have gotten away with it, using lithium grease on straight threads but, I haven't done a pipe thread.
Machining them down, is also problematic and you'll need a pipe fitting to screw them into. If the small end needs to be shortened, you'll have to turn a step to hold it, on the big end first, flip it around, shorten the small end, then put it back in the pipe fitting to shorten the big end.
Measure carefully, since the thread is on a taper, it's easy to miss your mark. Screw it in, 2 or 3 times, with the torque you want to use first, before measuring.