Hey y'all, here's what I have going on:
2012 Nissan frontier, 2.5l. Had a blown head. Tore it down, had the valves done and the head checked. Was running before the tear down, just terribly. Pulled the motor for the tear down.

Put it all back together, triple checked timing, I'm sure its good. But when I initially was plugging everything back in I had the engine harness all twisted up and plugged the Crank Sensor into the Power Steering Pressure Switch. The truck started and ran, but very badly, and quickly died. Then it went to crank no start. It would occasionally fire once and, but then just crank. I found my mistake and fixed it, and now everything's plugged in properly. But I still get the occasional fire on one cylinder and then endless cranking. I pulled plug 1 and tested, I'm not getting spark. Googling and searching forums, I see that loss of crank signal is a common cause for no spark. I pulled the EC manual from the Service Manual section and checked all the wiring for the Cam and Crank sensors. It all seems good, no shorts, power where it needs it and ground where it needs it. I replaced both Cam and Crank sensors for good measure, no change.

My current worry is, is it possible I blew my ECU? Looking at the Power Steering Pressure Switch, it gives some voltage (1-4v) on pin 2. But I'm under the impression the crank signal on pin 2 is also voltage? So that shouldn't be it.

Besides this, any suggestions on what to check next?

It's not likely you hurt the ECM, but it's very likely both sensors are toast. Power and ground are reversed on those two connectors, plus the crank supply is 12V while the PSS supply is 5V. I doubt either one would have survived reverse polarity. However, it is also possible that the 12V on the PSS ground pin could have harmed the ground bus inside the ECM.