Does anyone have the specs on these, valve, combustion chamber, runner size, how well do they flow. Could you compare them to an AFR ??

I have no idea which head that is, but my Performer RPMs flowed at .700 lift in335 and ex244

pretty much aluminum version of a gm rect port head,not remotely close to a good afr head.

Read up on them months ago. Conclusion was there were designed to merc specs and nothing special. Thought they were 310 runner. I was gonna use them on some long blocks to sell but decided not to.

pretty sure the only thing different from the non merc head is the exhaust bolt location on two bolts holes,that way merc thinks they can sell replacement heads.

Yup. that makes it proprietary. And thus mega money. LOL.

I bought a pair of 525 long blocks assembled, Im wanting to make 600 ++ hp from these with a Vic jr. intake and a 850 carb is that reasonable ?

Would a different off the shelf cam be better the same springs ?

I think a good estimate will be near 570 -580hp. From what I've seen the AFR's should put in another 30hp or so.

Here is some flow data on the 315 Edelbrock Performer RPM heads.
http://www.airflowresearch.com/bbc-shootout/

PS: if you get fixated on the hp/tq #'s on this article, remember it's got a solid roller and just use the power #'s to compare the heads.

dart now has a cnc'd head for the 525 I believe.

http://dartheads.com/dart-product/pro1-24-525-mmr/