I can't offer you a lot of insight, but I am in a similar situation. I have a '51 that was built with a 216, but it is now sporting an old splash-oil 235. Because the 235 is so old, I am assuming that the swap was done either right when the truck was new, or within its first year or two. So swapping out a 216 right off the bat isn't completly unheard of.
Rob
