Resolved: that 3-hole pump is a marine inboard engine pump. There is absolutely zero need for that third tap in an automotive application and it is NOT the discriminator between being an A/C or non-A/C water pump.
The irony is that this pump was specifically listed for A/C applications and yet it absolutely will NOT permit mounting of the A/C condenser bracket but, as we can see on Toad's 273, there is no reason you can't use it on an non-A/C car.
So....I got Rock Auto on the phone and had my order number ready to go...no small miracle since the order was filled 16 months ago and, as such, I had little expectations of the vendor actually doing anything at all for me. I told them, "hey look - these car projects often go into extra innings and I am just now getting around to installing the pump I bought nearly a year and a half ago but it turns out that this is a no-fit item -- what can you do for me?" Believe it or not, they did do something. I am getting half of what I paid for it back in store credit. Not bad considering the time elapsed. Its going to be emailed to me in the form of a coupon code and once I get it, I'll turn around and order another pump. So, project is on delay. Considering they are coming to rip out and replace the flooring in our crib...the timing actually works well for me.