Got some info:

There are two good heads for the 289 with the c5ae# :

If there is an 'HP' designation stamped on the head it is the high performance head. If not its the 289 4V head with the same compression chamber. Put 3/8" studs and bigger valves and it's the same as the hi-po.

had a mustang show in town and i asked a few in the know....? I'm assuming the HP stamped heads are gold and the 4v silver regarding value...neither bad.

 

One good way to tell the diff is that the Hi-po heads had machined valve spring seats to prevent the spring from walking in addition to screw-in studs (which can be easily added to non-hi-po heads.)

I once had a set, didn't really know the value of them and sold them to a buddy for 200 bucks...