Saw a GMC 350 'toter today

[greywuuf]

and I need a history lesson.
I USED to have a "first series" 55 chevy the one that looked like a 54 but was built in 55 and came with a pressure oil system.... anyway, I used to know the cut off date for turn down vs push button Door handles at least for the chevies. Ok now I need to know some date specific features of the older GMC's as I saw a Very short wheel based Dually that was a mobile home toter "back in the day" it was WAY cool and I am trying to decide how bad I want it.
I was at the house picking up something else and was very busy so did not get a good look at it as it was in the back 40 and pretty covered with stuff, but it did have turn down door handles ... a 350 (series) emblem on the hood and it is available.

What engine should this thing have in it ? anyone familiar with the heavy GMC's

Thanks for any info and discussion.
Dan