I would curious to see the digits stamped in the block right by the temps sensor in the head. That would almost always tell all.
The cast in lift hook in the first pic is only on 1966. Red mid-sump oil pans usually mean it's a 425, but the '-705' casting number is on 401 blocks. As Larry replied, check the ID stamp just in front of the valley pan.
66 401 with 425 or 66 Skylark GS heads? I can't see any color on the block? I did read from Russ Martin they bored the 401 705 blocks to 425 in the day??