4A-C

[banpei]

All A blocks fit, so a 1A, 2A, 3A, 4A, 5A, 6A, 7A, 8A and 9A have the same shape, but only some of them share the same bore: the 4A and 7A have the same bore and only the 9A has a larger bore.
We have seen 3AGE and 7AGE engines so far and some people swapped 20 valve heads on the 16 valve blocks.

However not all blocks have the same strenght (3 or 7 ribs) and if you want the same performance out of the 4A as from the 4AGE you may need to swap the crank as well: it is weaker than the 16 valve crank.