Stage 1, 0016 will have 2 bolt mains, a converted stage 1 will have the remains of a oil pickup boss directly next to #2 main cap. It has to be machined away to clear a 4 bolt main cap.
Early casting stage 1 blocks had 1 water passage cast in the deck next to the middle 2 head bolt holes on the upper row. 9 times out of 10 a stage 2 will have 2 water passages next to each other. The only exception i have seen is a 0016 block and they came either way (one or two water holes).
I have a few blocks here, i can take pics if it will help you out.