Sorry to borrow your thread alan600.

In most cases, when purchasing aluminum heads, you can not use the stock / standard 7.8" SBC pushrods. Why? Because the rocker will not rub the tip of the valve stem dead center. The cyl manufacturer states that in most cases a 0.100 longer pushrod is needed for correct geometry. Verify with checker.

So. Where does the extra 0.100 distance come into play? Where is the extra height of the rocker that requires a longer pushrod?
Is it the rocker pad itself is higher?
Or is it the guide plate raises the stud that much?
Or is the actual cyl head 0.100 thicker / higher? I don't think so.

 

I just said in the previous post where the +.100 comes from....valve length.
The only thing that will set rocker arm geometry is the pushrod. The only thing that changes rocker arm geometry is valve length ON an adjustable setup. The stud, guideplate, and rocker pad DO NOT and CANNOT change geometry. Now if for some reason these offshore heads have the stud boss move in or out....this will change it.
My best guess is they tell you to go +.100 to avoid crashing the trunion/ball on the bottom radius of the stud....but this in itself WILL NOT determine geometry on its own....
Like I said....my last two small block Vette’s wanted a 7.850 pushrod....one is a Dart head, the other a 461 GM Camel Hump.....
The +.100 number was most likely created by the bean counter to prevent call backs that **** doesn’t “fit”.
The countless solid roller setups I have done want a 7.900 or longer pushrod....this is because the valve is that much longer....
Now on a Jewel or T&D, pad height is everything....you can fiddle with pushrod lengths and shim the rocker off the pad to get optimum geometry....
On an adjustable...the valve and the pushrod are the two ends of the fulcrum....the stud/nut just holds the pivot...
I believe that my 7.850 pushrods are because I like to run 1/2 turn on Hydraulic stuff for lifter plunge....GM want one turn....this would make the pushrod have to be shorter in order to have correct geometry. This accounts for .025, the other .025 I believe is rocker pushrod cup.

Jebby

Jebby

 

Would not use an EX cam for anything you described or for long term use.