Need some help figuring out a no start '91 Prelude SI

Hey all, hoping someone here can give me some better answers than anything else I could find. Got a customer's '91 Prelude SI in and it has no injector pulse, no power to fuel pump, and no spark. The car came with the B21A1 and ECU wiring matches 2.1L wiring diagrams, as does the ECU itself (PK3). But, it has a B20A5 in it and am not sure on if this ECU will work, and if not, what needs to be done to get this car running. 2.0L to 2.1L diagrams and pinouts for the ECU are different which is why I'm asking. This ECU is not grounding my GRN/BLK wire for the main relay, so that arm is not flipping and as a result not sending power to my fuel pump. I can ground that wire at the relay and when I do, my CEL comes on kinda dim, the speedo starts moving some, and the little red LED in the ECU comes on (does not flash). The car still doesn't start though. If I don't ground that wire and leave it as is (it's giving me ~11V key on), I have no CEL even during bulb check, and no codes flash from the ECU. As for no spark or injector pulse, I'm kinda lost. I'm not sure if there needed to be some wiring work done before the 2.0L could work in this car due to the different ECU pinouts and if that is necessary then I'm not sure if this ECU was consequentially fried. Anyone have some input/help? Is there wiring/pins that need to be fixed or does this just sound like junk ECU? Too many variables for my liking and if at all possible I'd like to be a bit more confident and have more of a definitive answer before selling an ECU or whatever other work it might need to this customer. Any help appreciated, starting to pull my hair out a bit with this.