[steve25]

You will need some porting work to be done with either casting to hold onto 600 or better hp @ 7000 rpm since on average these heads flow 225 cfm, and a science out valve job can get them up to 240 cfm which is still only enough for making some 490 hp .

The 614 casting has a slightly lower port angle and as such when ported flows bigger Intake numbers particularly at .200" lift .

This is where you want the head head to flow big numbers like 145 cfm@28" of better( with numbers of 155 being great ) since that with the addition of a good tuned Exh system allows for high VE numbers and a slower nosing over of peak HP numbers also!

The highest vacuum you see in race motors that the Pistons can pull at wide open throttle and at 5% before the rpm of peak HP is 1 psi, a tuned Exh system with a merge type collector can apply 8 psi of vacuum before the Intake valve has opened and piston has even started its travel down the Bore!!

The placement of the overlap in the Cam you use will also be a big factor in success!

Here's a graph of in cylinder pressure readings of a 600 hp motor @ 6000 rpm plotted against a bunch of factors, it looks confusing but really isn't!

Look at the Red line and note the 180 degrees of the Intake valve opening cycle, note on that red line that the peak depression in the cylinder is 100 inches , yet the valve is only open some .075"!

That 100" depression is make by the Exh system creating and negative pressure wave that goes all the way back into the cylinder, and in case you have not noticed, that negative wave is nearly 3.6 times the common depression we test with on a flow bench!

At .200" lift the depression is still over 50% of that max of 100 inches!
You posted about having to run a duel plane Intake , does that have to be iron also?
This all assumes that porting is allowed of course.