You're carbed on an '84.
Since it is now 25 years old, it would be emissions exempt in most areas.
And also since it is an '84, you're going to be changing out the transmission anyway.
Therefore, I'd go 5.0. Easier than 4.0 if you decide on a carb, wiring will be the same amount of work as 4.0 if you go EFI.
For the amount of wiring work it would take to put a 2.9 in, I wouldn't think of it even if the 2.9 was free. Only way I might consider it is if I had a complete running 2.9 BII to swap EVERYTHING over from.
Too many 4.0s and 5.0s around for reasonable prices. (I paid $75 for my complete 4.0 with 38k miles on it.)