Heads:
All 2.0/2.3/2.5 heads will physically bolt in place of each other. They all have similar exhaust port shape and placement. All cams are interchangeable as long as they are used with the proper followers. Later model (1995 and newer) roller cam followers cannot be easily swapped onto an older head as the valve stem size was reduced in the newer heads and matching slot in the follower was reduced. Early 2.0 and 2.3 heads have the same small round intake ports spaced evenly apart. They differ from each other in their valve sizes though.
Head Variations:
There are several variations on the 2.3 heads though they break down into (4) distinct types:
1) Passenger car oval port heads - 1974 - 1980 Mustang, Pinto, Fairmont, Bobcat, etc.
2) Passenger car D-port head - 1981 - 1995? T-bird, Mustang, Etc.
3) Truck round port - 1983 - 1988? Ranger
4) Truck D-port - 1989 - 2001 Ranger. The 1989 - 1994's and 1995 - 2001's have different combustion chambers and ports. It is thought that the newer head is better designed.