If I bought a 1985 manual ranger could I put my 1990 2.3 four cylinder in it?

 

Sure
Unless the 1985 has a 2.0l or 2.3l gas engine you would also need a 2.3l manual transmission, transmissions are not interchangeable they are engine size specific, but if the 1985 has the 4cyl Lima engine then it will work with the 1990 Lma engine
You also need the 1990 computer and most of the 1990 engine bay wiring harness
Also the cross brace in engine bay for the 2.3l drivers side motor mount