Have you checked your timing marks since you put the engine in? id try resetting the ECu once pull the pos cable and let it sit.
My thought was trying to reset the ECU too. Don't forget that you shouldn't touch anything for the first 5 minutes after starting to let the ECU work out it's parameters.
Having the second O2 sensor would help out too.
My other thoughts are that your fuel pressure regulator might be stuffed. Or there is something between the donor vehicle and this one that you're missing.
It really is a guessing game without being near the vehicle to physically check it out
All the best (subscribed)