I did read through the FAQ's here, but they seem to have aged before the "Glock Mag era" of 9mm AR lowers got going.

Reason being, I just finished a 3D print of a 9mm Glock compatible AR lower, (A "Gluty" designed by "Warfairy" and came as part of the DEFCAD/FOSSCAD mega-pack .zip file download) and it's already doing well with test fitting of an A2 grip, ETS Glock magazine, and a KAK buffer tube and Sig brace I had laying around from stuff I'd F4'd and SBR'd in the past few years...

The design does not include a BHO lever, or the slot for it, but I don't mind and I at least know the lack of that won't interfere with anything. However, it does not have a slot in the main solid web between the FCG pocket and the magwell for an ejector either.  Are there 9mm AR style uppers that use a bolt with an ejector in it like the 5.56 bolts?  

I'll just print more lowers as need be, modify the files in CAD to add the slot and some holes for a few pins and set screws to keep it from wobbling. Thanks for the tip on the NEA ejector. $3.99  is not much to pay just to help with fitment. I can take measurements from a friends 9mm lower.

Documentation was sparse for this, and I'm trying to figure out, all while "Not knowing what I don't know".  I've built 4 AR's in 5.56 and .300AAC, but haven't jumped into 9mm or .22LR ones yet.  The lower and how it printed as-is is probably all just for the "Shuty MP1" pistol where most all of it is printed then. On that design, the ejector is in the upper, which would make sense then as to why there's no provision one for a lower.

I think researching through all the various 9mm lowers out there, I got confused, because some websites show theirs without the ejector but list it as included, some have the large angular New Frontier looking ejector, and others have a thin curved finger of an ejector. So I'm correct in now surmising that most all 9mm AR lowers have some kind of blade-like ejector or ejector finger in the web between the FCG pocket and the magwell?  

There are probably other variants of this lower file that are set up for a more standard 9mm AR upper. The DEFCAD/FOSSCAD mega-pack is several gigabytes in size. So I'll have to do some more searching in there.

Thanks! I'll try that too.

This first receiver is going to be a full on Gluty/Shuty MP1 now. I've gone and printed the really hard part, the upper for that, a whopping 58 hour print.

But I'll print another one of these lowers once the MP1 is done, and get a 9mm upper running on it.

All valid points, but... I can always just print another one.

I've now gotten its Glock barrel pressed in, I'm trying a shorter threaded G26 barrel first, despite the Gluty/Shuty's creators having it spec'ed for a G17 length barrel. I'm hoping a shorter barrel means less back-pressure, which means I could get away with mounting my Gemtech 9mm multimount on it and not screw up the timing of the basic blowback action too much. In theory blowback is pretty tolerant of a wide range of bullet weights or pressures, since the chamber obduration/swell of the case while firing, combined with bolt-mass/inertia and spring pressure is what keeps it closed, and higher pressures mean the case stays "stuck" longer, but that goes only so far. And I don't want to press my luck for obvious reasons.

If not, I'll press it out and get a Lone Wolf one.

I still plan on trying a factory 9mm AR upper on the Gluty 3D printed lower, but since everyone's given me some good advice and things to look for, and what the challenges might be, the least I can do is keep you posted.