thread renovation ?

[hardtimes]

I'm working with antique aluminum parts, removing brass plugs frozen with time 80+ yrs time. Feeling lucky to have removed some parts, so far, without breaking any casting. Aluminum oxide has made the bond and has indicated that the aluminum threads should be cleaned.
If I do not have right sized taps for the, too large hole, do you know of any way to clean these alum threads without damage ? I will put some lube on reassembly to help prevent recurring problem.