What do i have here...21-stud hybrid ?

[flatheadmurre]

So what do i have here ?
Some kind of later replacement block ?
It has the early front that will pass a pencil test.
Later exhaust outlets that are not sticking out a lot.
Raised intake deck.
I have bored it 3 3/16 and it has a LOT of meat left...i think it would take .125 more and be .100 left in the walls...have to ultrasonicly measure it.
Looks like a hybrid replacement to me...would be great if anyone can verify what it is and year of manufacture.
The 2 blocks in second picture is one normal -37 left and the odd 78 block right.