A few people make adapters, but the original thread is short and designed for the castle nut. Somewhat leery of the thin barrel and short threads holding the suppressor in place at supersonic pressures and rapid fire... plus it would likely be overgassed with supersonics. Then the twist is still a limitation with heavy bullets.

Might be a major project. For the record, I have never suppressed an M1A, so YMMV.

Tom, before I got into .300 blk for subsonic shooting, I was loading subsonic .308’s with trailboss powder. It worked excellently!

I love shooting suppressors. I’m looking forward to ‘hearing’one Of John’s cans some day

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https://facebook.com/M2bKydex/

is an exercise in frustration control.

Delta P Design and Smith Enterprises are the only two manufacturers that make serviceable adapters to keep the front sight at the muzzle and provide a standard 5/8 X 24 thread. Delta P is Titanium while Smith's is Steel, but either will do the job.
Grizzly Gunworks makes a thread adapter, but you lose the front sight (no big deal if you're going scoped).

However!

The thread pitch on the barrel for the castle nut is 595 X 32 NS and the main problem is that Uncle never had a specification for absolute concentricity of the thread with the bore. Civilian Springfield Armory and other MIA manufacturers never seemed to care either.

You are at the mercy of the unknown machinist who threaded the barrel and what you have is what you get. If the threading is 'off', the adapter and thus the suppressor will not be aligned with the bore and you'll be tempting, at best, a baffle strike and at worst a blown can. And there is nothing that can be done short of cutting the barrel back having the threads cut on a lathe.