Couple of things:

I tried running it up until it seemed to nose off, backed off, then floored it again. Every time I did this it got up to around 4400-4500 rpm and started making an angry ping pong ball noise that sounded like detonation and power fell off with a "stop flooring it" type of feeling. I don't know if I ought to not be running 87 now or if it's getting so lean up top that it's pinging (maybe holding a higher RPM at lean-ish mixture heats the cylinders to the point of detonation will happen at higher RPMs but not when running it up in one go? I dunno, maybe something was rattling), but that's what happened.

I also tested my fuel pressure and I'm getting a good 6.5-7 psi at idle. I couldn't get my dang metal tees to seal well enough at driving RPMs in my garage to be comfortable actually driving with the gauge hanging out from my hood, but the pump seems strong.

My guess at this point is that the carb is just too low-capacity and too lean for the amount of air I'm trying to pull through it at this point. I'm all set to put my 650 Carter AVS on save for an air cleaner and a pressure regulator (didn't expect to have such a He-Man old pump but I sure need one now) so I'm just going to go ahead and do the swap and see what happens when it can get more fuel down.