IIRC (was a while ago I worked with acrylic) it takes a tap pretty good,

I'd bet that's the case. The screws wound up just fine -- nice grip actually -- but might have tried machine screws if I had short ones on hand. If I did that and had the glue gun warmed up, I'd probably squirt some glue on them by way of an ersatz lock washer.

Now if I can get digital output soldered...and get more Brian buttons...I'll be having fun!