sidedraught,
for example ,the gx head is known to outflow any other production car a-series head.this is under assumption that both are either stock or both equally modified and running similar setups.

http://datsun1200.com/modules/mediawiki/index.php?title=AY12_engine

According to this link in this forum, the ay12 were 160ps @ 8800rpm and Racing trim was reportedly 220 gross horespower.under 1300cc class,220hp gross hp(reportedly) is no easy feat! Same cross-flow head on a larger capacity a-series and one can only imagine...

which questions where the power figures came from as its a very rare engine.so only either info from nismo/ factory works or owners of cherrys or 1200s with ay12s can be more credible.better yet a dyno graph with a list of mods attached to it.how many ay12s were produced?

also from link above

Benefits
Using a stock A12 engine block, here are some benefits of the racing-only A12Y cylinder head:

1.It is crossflow, the inlet and exhaust are on opposite sides of the head.
2.Using a hemi cylinder head design, the valves are in better position than in the normal model. Racing trim was reportedly 220 gross horespower
3.The is no heat problem with twin carbs, because they are on diffent side than the exhaust manifold.
4.The chamber is hemi, it can take more compression without unintended pre-detonation (knocking or pinking/pinging)
5.The exhaust side is the same as normal head. The ports are not in same place but one can use standard A12GX exhaust manifold