Had a customer send me that exact rifle along with an APA Gen.1 Micro Bastard (1/2").
Had real reservations about doing it- called APA and spoke with him about it, at least at the time (this was a couple of years ago) they were routinely doing it on their own customs with similar skinny barrel OD's. I did the job, never had any issues after but...really didn't want to take the risk.
As said barrel wall thickness is extremely iffy. Had he not already purchased the brake, my preference would have been (and still is) using 9/16" here.
I'd rather have more meat around the bore to avoid "swelling" which I've seen with really skinny walls. As long as I've got some shoulder to align the brake correctly and use Rocksett or red threadlocker to make sure it can't move.
JMO.