My 79 van is a B-300, and my parts unit is an 81 B150. I think they changed the rating numbers in ~1980, about the same time they went from 'sportsman' to 'ram'. I suspect this is the same in the trucks as well, just a model designation change only. Seem to recollect my Hollanders saying the suspension parts are mostly the same, with some upgrades in 1978-79.
