Hemi ECU / PCM Confusion Questions

Hi everyone,
I've been looking into the possibility of using a modern hemi (and there are a FEW local to me for sale from$100-$250) in front of the 904 or 727 i have or even possibly get a A833. I don't want to deal with the fab work needed for the 545RFE to fit. Where confusion comes in is the electronics for the motor. I've read different things and I feel I read to the point where its all now a blurring together lol. I'll break it down what I think I know and what i'm questioning:
-I know you can use factory computer and electronic stuff with a hemi/trans swapped from a truck. I've read some posts about it.
-I thought I read that just the hemi will work alone, provided the hemi is from a standard truck and from a certain year?? Not sure about that one.

I would really like to just use the new motor and its factory electronics only. I have no problems with modding the factory harness.

Any direction /help would be awesome.

Thanks!!!