Second 70, good info there. Also, I agree with the Zippster that the siamese block was referred to as the megablock and the waterblock was referred to as the waterblock or sometimes the "replacement block".
Another note: the earliest MC castings have the area in front of the oil pump mount profiled similarly to the original block. So they are more desirable for restorations. At some point (still pre-World) they started making that area flat, a dead giveaway that it was not an original block. In the following pics, the orange block is vintage, the grey and the bare are the earlier and later Motor Casting blocks