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I ended up buying a 16188051 from a 1995 Impala SS. I got it from a yard in Kentucky for $90 w/ shipping. They also threw in the harness with a foot of wiring. I have the wiring diagram for my 1995 Vette and found the 1995 Impala SS wiring diagram online. The biggest concern I had was one or two sensor grounds on the Impala were purple instead of black- once I got the wiring diagram, it made me more confident of hooking everything up. I basically connected all the grounds togethers into one wire (black negative arrow in the pic) and all the power sources into a second wire (red positive arow in the pic). The serial line was just a single wire. I bought an OBD2 connector off Amazon and wired the 2 grounds to the bundle of negatives from the harness, the positive to the bundles of positives from the harness, and the serial data line to the serial data line of the harness. I connected the positive and negative wires to a 12V battery that I made sure was charged up and plugged in my ALDL cord to the OBD2 connector and the USB end to my computer as normal. I first made sure I could download the existing Impala bin. Once that worked, I flashed my latest Vette bin to the ECU and it worked!

I then swapped the Vette 16181333 for the 16188051 Impala ECU and kept my fingers crossed. Everything worked great. What really surprised me is that the tach and oil temp gauges worked since the Impala didn't have those outputs. Pretty cool having a backup for cheap and everything is working. The one I'm not 100% sure about is the ASR spark retard since the Impala doesn't have that and it looks like other F-bodies have that signal on a different pin vs. the Vette. It doesn't really matter to me since I always turn the ASR off. The Vette seemed to drive normal and no weird ASR issues- the engine is a 383 and the ASR doesn't like to play nice with all that torque so I always turn it off.

Thanks again for everyone's advice and hopefully some of this extra info is helpful to others.