hes prob going to tell us you cant weld spider gears in you axles
what it sounds like you are confused because welding spider gears
can be done (as opposed to this which can
not be done) but like this case welding spider gears and trying to swap a 2.8 in place of a 2.9 just because the 2.8 was free..........you just want to save a buck. that's why anyone ever welds spider gears too. they're too cheap to spent the $100 to buy a spool which is stronger. don't let your cheap-ness negatively affect your truck. by going backwards from a 2.9 to a 2.8 (the reason the 2 are so different is because ford re-designed that crappy engine that had mechanical, and oiling issues, as well as lacking severely on power), and if you do don't let your cheap-ness let you go backwards from efi to carb just to "make work" the wrong engine
just because it was free
and oh yeah, if you did that it would be breaking a federal law punishable by $25,000 fine (never seen it actually enforced. but just one more reason)
and no amount of "working harder to make something work" is going to make intake runners line up.
now if you're done not getting it (which i bet you're not) let me tell you how i would do it. get the 2.8l complet, and i mean complete exhaust manifolds accessory drive (i.e. alternator, a/c compress, p/s pump, they all mount differently)
install it. then go to the tech section (or just search
) about installing the 3.8l throttle body on to a 2.8. ignore everything except where to get it, and how it attatches to the intake manifold.
next, take one of your injector plugs from each side of the engie (the 2.9 is bank fired just like a tbi so it only h as 2 injector drivers in the ecm anyway)
and attatch one to each of the 2 injectors on the throttle body.
you'll need to adapt the fuel lines from the 2.9 to the tbi. but
i'm sure that you can "work harder to make it work"
and of course just re-connect the sensors, but since a 2.8 was carbed i'd bet you'll need to "work harder to make it work" by adding sensors to the 2.8 that were on the 2.9........not impossible
i think that the only deal breaker is that you may not be able to use the 2.9's distributor which has the cam position sensor built in
all that or just duraspark it and leave the 2.8 carbed