Re: 2.0l to a 2.9L
You're going to need the bonco as a donor for most of the stuff, like the engine wiring, computer, transmission, etc. Will also need to find a set of Ranger EFI fuel lines from a similar truck. There's a lot to an engine swap, especially going from one type of fuel management to another.
It's been said that the 2.9L can be carbbed in theory, but I've only read about once instance of it begin done. Basically you'd have to make either a new lower intake or an intake adapter for the carburetor and somehow retro fit a distributor like the 2.8L duraspark to work with the 2.9L. Then ignition module of your choice. Not unless you find some way to make the Offenhouser 2.8L work, I doubt it, but never had any 2.8L intakes to compare against the 2.9L. Same family, but they are very different.
I think I read somewhere that the 2.9L doesn't have equal length ports to the heads, but it doesn't need to with fuel injectors. Not sure what kinds of runnability problems this would cause, but then again that is just what I have read. Definitely would be a fun project and if completed, would piss off a lot of people, and gain the interest of a lot more.
1987 Ford Ranger Short Bed 5.0L/T-5 Project
1988 Ford Ranger Long Bed Parts Truck
1993 Ford Tempo 2.3L OHV HSC Auto - D/D Stock.
1999 Honda Accord VTEC Auto
2002 Dodge Caravan - 3.3L Auto