So got the speaker grill brackets from Marco, got the aluminum channels from mcmaster, got everything installed now. I'll be picking up the lift channel and top trim from pinball life on friday for the backglass but I can still slide the glass by itself carefully into the channels. I went ahead and printed a draft print of a temporary backglass on my printer (8 sheets of 8-1/2 x 11), so it looks washed out right now (especially with a single automotive fluorescent bulb shining behind it), but it gives me an idea of how it's going to look.
Speakers sound good and clear in the backbox (ran a test off my phone). Still not as much bass as I would have liked, but maybe down the road I can buy a separate subwoofer and split the audio.