The valley pan used on the ZL1 is
NOT the same part HBC sells. Here's an original (see below) 3931093, which was discontinued in 1990 and replaced by 14096974, which is the one HBC sells. the 14096974 pan was used on the 1990's 454 Electronic Fuel Injection (EFI) engines found on trucks, and is not even close to being correct for a ZL1, which is probably why it doesn't fit. There's also the 12555320 shield, used on I believe the 502 (?). You can get this one from
GM or
SUMMIT RACING,
JEGS (although they show the CORRECT 3931093),
EBAY, etc... but it's not even close either.
But getting back to the OP's original question:
Did the L78 in 68 have an oil splash tray/baffle in the lifter valley?
The answer to that is no. And other than the 1969 ZL1,
NO 1960's Chevrolet production engine (big block
OR small block) ever had a valley pan from the factory.
Ed