If it's a '78 Power Wagon it will be full time 4WD with an NP203 transfer case. 1/2 tons always used the D44 front axle and could have had the 8 1/4" or the 9 1/4" Chrysler rear though the 9 1/4" was much more common. If it's a W200 it could have the D44 or D60 front axle and a D60 rear axle. W300 would have either front axle and a D60 if it was single rear or a D70 if it was a dually. Transmissions will be the 727 if it's an automatic or a NP435 or NP445 4 speed. The A320 3 speed was available but is almost unheard of. Engine options range from the 225 Slant Six to the 440 big block, though the reliable old 318 was by far the most common. '78 was also the last year for the big block engines. If you want more info than that, you are going to have to be a lot more specific about what you want to know. "Just general info" doesn't really tell us much.