There's one on auto trader, '85 3/4 ton 4x4 and it looks like it's a long box, is it a factory creation or some one throwing 3/4 ton axles under a 1/2 ton?

http://www.autotrader.com/fyc/vdp.jsp?car_id=204355286&dealer_id=66702&car_year=1985&model=&num_records=100&make3=&make2=GMC&start_year=1981&keywordsfyc=&keywordsrep=&engine=&certified=&body_code=32&fuel=&only_price=1&search_type=both&distance=0&model2=&make=CHEV&color=&min_price=&body_style=TRUCKS&drive=4+wheel+drive&default_sort=priceASC&max_mileage=&style_flag=2&sort_type=priceASC&address=54935&advanced=y&only_photo=1&end_year=1991&doors=&transmission=Manual&max_price=&cardist=698

Pretty sure they offered a 3/4T stepside longbed IIRC.

Yep theres a guy that comes and picks up block at work in an '80ish 3/4 ton longbed stepside. Chevys been doin it for a while too because I know where theres a '65 3/4 ton longbed stepside. The bed looks pretty utilitarian but not in a bad way IMO. It makes for a unique truck, you do a double take when you first see it.

It's begging to be a tow rig and my '90 6 lug 3/4 ton is begging to get straight axled and some 36's.