Dusty - 778 is not all of the number. Try cleaning the tag with a pencil eraser. Then hold a strong light to shine on the tag about 2 degrees above horizontal from the edge. It throws shadows in the stamped number.
If 9778, then it would be from a GMC 270, and probably is going to be difficult to tune well on a 216.
But not to worry. There are lots of dudes that frequent this forum that would swap you a GMC 228 carb for the 270 carb.
Jon.
