LA cylinder heads

Can anyone give me info & description of the small block cylinder heads cast with a "Z" on them? Are these a performance or non-performance head? Thanks.

Look for the casting number in the valve train area, date code too.

Possibly 915 heads, same as J, O & U heads.

Thanks for your reply........was looking to possibly buy an "A" body with a 340 engine........saw in the pics the Z code, so I have no way of checking under the valve cover.........

Z heads are 915 heads, the same as U & J heads.