67 C-20 pick-up

Hey Guys!
I have a 1967 C-20 PU. I think the engine has been changed. The block is stamped VT 003Y, it may be a crate motor or target short block. I'm going to sell the truck would like to tell the buyer what it is. I think it was changed in 1987 or 88. Any ideas?

Steve

get the numbers off the rear drivers side of the block that will tell the story. below and behind the dr.side head