Do a search on this forum for "vacuum four wheel".
I had posted previously some information that is still there on the vacuum actuator system.
You can improve on the OEM plastic hoses if you just use some hoses or maybe some bulk brake line tubing.
Anyway, some links:
http://www.automotiveforums.com/vbul...uum+four+wheel
http://jeep.larrynova.com/88/88_Tran...ith_vacuum.pdf
There are also kits to make the vacuum into mechanical using a cable actuation system.