What would be the best route......

I have an 88 Z24. It HAD a 2.8l v6 until a few days ago when it locked up. What would be the best route of action....
Should I just rebuild the 2.8 or drop in a different motor?
I know the 3.1 will drop right in without having to change the ecu or anything like that, but I was also told that a 3.4 will also drop in that easily but I am not sure. Also where would be a good place to find the motor at a reasonable price?

Does anybody have any clue as to what I should do here????????

Its all your own decision...