You still need the casting code and date code from the rear of the engine (near distributor) to be sure, heads are cast Nov 7 & 8 of '68 so if they are original to the motor and a YB code I would lean towards a B-body 400/265hp 2 barrel, but you still need to dig a little more...

The VIN is stamped in the same area as the block code but lower, I had to scrape below the radiator hose to find mine...but I am pretty sure it won't match anyways...