Hi Boss,
are you sure that it was a Holley 4778 that was specified in the supplementary parts list for GR3 and GR4? I think it only says List 213, which doesn't seem to correspond to anything, and everything I have seen posted seems to suggest great confusion about what the mysterious Holley 213 carb is. I speculate it is a date code and someone messed up when writing down the Holley model number and put the date code instead.
Cheers Tim