The 3.0 is a pretty decent little motor too, many would venture to say the toughest engine Ford ever put in the Ranger.
If you get a rollover for a donar, be aware sometimes they can run for quite awhile upside down... oil doesn't go in the right places with the sump sucking air and the oil on the top of the crankcase.
lol how did you find out 3.0s run for a long time upside down?
the 3.0 is not a power monster, but its still better at handling an auto than a 2.3 is.
the 3.0 is found in rangers starting in 1990.
so you basicly have 3 options
1-2.9L direct plug in and was used in your year of ranger
2-3.0L not to bad of a motor, tends to be more common in some areas, first offered in 1990 rangers
3-4.0L probly your best best, its in the same engine family as the 2.9, minus some of its issues, like cyl heads cracking when over heated, offered in 89+ rangers
seeing as you currently have a 4cyl, your gona want engine mounts too, you should go check out the "other engine conversions" section, lots of info!
good luck