36 EL head problem

I was starting up a 36EL that has been silent since the early 1950s, after a complete resto on the motor, the original front head had the common front head exaust port cracking, so back in 1996 I bought a set of the early FHP repop heads, had a shop put them together, they have set for 15 years while I worked on chasis and bottom end, and raised 2 kids, now I am back on this project, and the motor fired right up , ran it a few short times (not on the road) just testing in shop, cracks started showing up in the top of rocker boxes the rockers were hitting the boxes inside and cracked them, had a shop tell me the valve protrusion must not be correct, from bottom spring seat to top of valve is 1.5" I am told that is correct, why then are the rockers hitting the boxes ? stock lighting cam, stock pushrods, the pushrod ajusters are ajusted way up, like 3/4 of a inch up, that was the first odd thing that was noticed.
Any input would be appreciated.
EL rocky

If this machine is actually "Restored" as you state the original heads should be repaired and put back on it. Many times I see people who incorrectly use the word restored for a customized or just rebuilt machine. Which is yours?

Hi Rocky. Normally when there is an issue with stem protrusion, it is that the valve is too deep. Your symptoms seem to point to just the opposite. If the valve is not deep enough in the head, then the pushrod end of the rocker arm will start its travel from a point closer to the top of the aluminum rocker box.
Keep in mind that a stem protrusion measurement is dependent on not only the valve length, but also the thickness of the guide lip, thickness of the "spring cup", & thickness of the gaskets between the spring cup and head. If these parts are not stock, or to stock specs, then the stem protrusion spec will not be valid. That would be my best guess as to why you are having issues.
BTW, where did the 1.5" specification for stem protrusion come from?

Hello Lee, These are brand new (in 1996) FHP heads, the 1.5" measurement came from the shop that rebuilt the bottom end, when he had a binding issue on assembly, it had a bad rear exaust rocker in the heads another shop put together for me 15 years ago,and never ran, so he replaced the rocker and checked valve protrusion on rear exaust valve, and said it was 1.5", he also said the pushrod ajusters were way up? When I ran this motor it sounded good and ran good, however the rocker boxes started to show cracking on the rear, and then came the cracking in the front box as well, not as bad as the rear. I pulled the heads back off to inspect, I think the valve seats are not deep enough, I can not get a exact measurement on the protrusion with my digital vernier calipers, I think, and evidence shows they are less than (1.575) as I think they should be.
So the guy that put the heads together screwed up I believe,I would have hoped an experienced shop would have caught this issue on assembly
Thanks for the reply
EL Rocky