The first one you show is the 7 pin module (ICM) unit, yet if you look at Rock Auto they show the picture of the older 4 pin unit. When you read the description it mentions ... Without vacuum advance, even thought the picture shows its presence. So you have to be careful about just going to auto parts source to try to decide what you have.
The early CCC system was a very simple setup. The ECU read air fuel by the O2 sensor and tried to adjust fuel metering accordingly. The EST (Electronic Spark Timing) would adjust timing advance by reading the Knock Sensor. As spark knock was detected the ECU would retard timing by the EST. The ECU could also reduce spark knock by enriching mixture, but mainly first by reduction of spark timing.
This is why you can not put a non electronic carb on this setup and likewise you can not use a electric carburetor hooked up and use a Non-EST distributor and expect it to run correctly.
With your truck missing the harness, you will have to get a proper harness, ECU, Carb or TPI or TBI and Distributor and all the other sensors for that year. All of it will have to work for your engine and transmission combination.
Depending on where you live, you might be able to go stand alone (Non-ECU) Carb and Distributor. OR maybe not...
Back in the late 90's and early 2000's there were several conversion of TBI and TPI 305 and 350's being put into all kinds of things. Plus your 87 would have come with a truck (K) 700R4 which was highly sought after. This could be why it was gutted and harness removed. Quite possible there is a 72 Nova with a 305 TBI/700R4 in it and it wouldn't be much of a surprise to see that or similar.
So anyhow..., check with local laws and from there decide what to do. The gutted 87 is an easy swap for 305/350 with a TH350 or TH400 or 700R or 2004R. Or LS Swap with a 4L60E/4L80E...
