swapping the shift fork is not that big of a deal, it's only 4 bolts, and a couple little clips. And, in order to swap the shift motor/actuator, you're going to have to pull the CAD housing anyway, which will expose the shift fork, colar, and axle splines.
anyway, are you positive that the axle is not engaging, and that it's not just a burnt out bulb?
first, make sure that the T-case is engaging, with the engine off, shift the T-case into 4wd, and crawl under the jeep and see if you can turn the front drive shaft. if you can, then you have a T-case or T-case linkage problem. if you can NOT turn the drive shaft, then the T-case is ok, and you can move on to the front axle.
jack the passanger side front tire off the ground (block wheels, and support with a jack stand),
with the engine running(transmission in park or neutral) and the T-case in 2wd, make sure that the passanger side front tire can spin freely. Then put the T-case into 4wd, and try to spin the tire again. If it still spins, then you have an axle disconnect problem.
Sense you already checked the hoses, the next thing would be the vacuum switch on the T-case. You can test it by disconnecting the vac lines from the front axle, see which line has vacuum when in 2wd. Then shift the T-case into 4wd. The vacuum should switch lines. If it dose, then the vac switch is ok.
If the vacuum switch is ok, the only thing left is the vacuum actuator(motor) on the front axle. like I already said, it's only 4 bolts to take it off, and then you can inspect the fork, colar, and axle splines to make sure they are all ok. also, wile you have the actuator off, if you have a hand vac pump, hook it up to the actuator, and make sure that it moves, and that there are no leaks in the diaphram.
maroon 1987 Grand Wagoneer. stock for now...