Re: 2.9 help
Performance isn't easy or cheap.. Like most, heads are likely where you're going to see the most improvement.
Cam is going to need to be a custom grind, cam craft has RV cams (might be able to grind one for you), Colt Cams in B.C. does it, or just ask a mfr if they will do it. And you would want new springs that match the cam.
4.0L valves w/ machine work
I heard that 390ci Ford lifters would work (but I haven't tried it).
Free floating rocker arm conversion.
Could have ARP rod bolts installed and have the rods shot peened for additional strength there.
Mill heads to bump up CR, but intake needs milled to compensate also depending on how much is shaved off.
If too extreme - you'll need to swap up to a '90 California Emissions computer to use a MAS instead of a MAP sensor, or else it just won't run well.
The only roller rockers I have seen were made by CamCraft for $550 and had a 1.55:1 rocker ratio. Very nice, just a big chunk of change.
Think Tom Morana has some stuff too.
There's a book out there by Sven Pruett that covers 60 degree Ford engine performance, but very hard to come by. And a lot of the mfr info pertains to manufacturers that are no longer in business.
You already have the 58mm TB, but it's possible to swap a larger TB from a 5.0L, but I don't think you'll need anything that big.
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