426 Hemi i.d. pad

Could someone decipher this for me, the cast date on the side of the block is 5-4-64.

That is a V=1964, H= hemi, 426 cid and a HC= high compression.
the 6-1 is the assembly date. That cast date is a little earlier. You have a 1964 race hemi block. It worth some money to guy wanting to restore one of those cars.

Thanks, do any of the other markings have any significance ?

I think the 08 stands for 8th motor that day

WT= Water Tested. I appears the worker had no "T" (or didn't bother) and used a dash twice to make the T, but I'm no expert.

Edit: The big circle with the two numbers (kinda looks like somthing-3) I could only speculate.