Block casting # 2128418-6, can't find on any list

I have a slant 6 out of a 67 barracuda, the block casting # is 2128418-6, I cannot find this number on any block casting charts anywhere, the #s are cast into the drivers side of the block in 1inch numbers, I'm about to start a rebuild and want to know exactly what I have, can you help me figure this out

2128418 is the actual casting number; the -6 is just an internal reference code that indicates things like which set of casting tools was used, which engine line/shift it came off, etc.

2128418 is a first-year (1960) RG (225, could also be made into 198 with the right crank and rods) engine block. You should find an engine stamping number behind the water pump or, if it's a late-production '60 engine, you might find such a stamping on the block deck outboard (passenger side) of the frontmost cylinder. I wonder if you've found any adaptations in equipment mounting; the '60 blocks and heads weren't set up to accept the '61 and later passenger-side alternator mounts, for example.

^^^ That is pretty interesting about the '60 accessories.

One minor thing in the '60-'62 engines is the orientation of the piston oiling hole in the connecting rods. They point up at about a 45* angle. On the '60-'62, they pointed at the cylinders, but later, they were pointed at the cam side of the block. Apparently they oiled the pistons too well. Much later, they were removed. Our '62 had them re-assembled towards the cam side.

Long discussion/debate about the squirt holes is here (pop some popcorn).

Another bit of trivia: if your cylinder head is also a pre-1963 item, you do use the metal ring washers on the spark plugs. If it's a '63-'74 head, you do not use the metal ring washers—see here. ('75-up heads use taper-seat plugs)