The Vehicle Engineering and Manufacturing Company of Fort Wayne Indiana offered Ford and Chevy van conversions from approximately 1976-1980, and went out of business soon thereafter.
http://www.curbsideclassic.com/blog/cc-outtake-1980-dana-v-drive-4wd-gmc-school-van-a-rarity-indeed for the full post and article about it (thanks Mike!)
the online patent http://www.freepatentsonline.com/3814201.pdf
Developed by Dana in the 1970’s, the V-Drive system was originally designed to add 4-wheel drive to Chevy vans, Blazers, and station wagons and to keep the drive height low. The idea didn’t catch on with Chevy, so someone allegedly bought the rights and started the Vehicle Engineering and Manufacturing Company (VEMCO). The company was based out of Fort Wayne Indiana and did 4×4 van conversions. Ironically, if you look at the patent, the inventor Loren James O’Brien was from Fort Wayne. Coincidence? These V-Drive systems found their way in to both Chevy and Ford Vans from 1976 to 1980. http://www.blueovaltrucks.com/tech-articles/axles/the_vemco_v-drive_system/