I believe the original engine for this truck was a 270 which from what I've been reading uses a block built by Atlas in detroit which was the same as a 235 but with a little taller deck height and larger bore and stroke. The 56 I looked at had the 270 in it and it looked like my 235 only with a different valve cover, 2 bolts holding it down as opposed to the 4 bolts on the side of the 235. All this may be a blessing as it may be easier to get 235 parts than the 270. I have a Chevy grille in it and I think I have the 58 GMC grille only it has a cross piece missing off it. If I can find or make the cross piece I may change it for the GMC look since I have the little 100 emblem that mounts on top of it. Might be nice to have that GMC look.
