[Short 3/4]

Easy way to tell 250 from 292 is side covers are taller on a 292 (6"). If shorter it's a 250. Both great engines. The 292 has more power, but the 250 will wind out a little further, which you may prefer as that truck has some really low gears, probably 4.56
Enjoy your new project, keep it simple and refurbish original parts whenever you can and you will have a lot of fun and learn a lot.