Picked up a set of these mounted on 324 rocker shafts. They were suppose to be from a J2 engine with the dimple covers that debut with the Nascar J2R engine. These are in excellent shape but I have nothing to compare them to for verification.
I know that back in the day one of the things seen was the adaptation of the Studebaker adj rockers for the early Cad V8's and supposedly the early Olds as well although it has been said by people in the know that they are not suitable for the Olds.
In addition, it has been said that Isky may have made the rockers for GM. I believe there were 500 J2r's made according to what I have read on the web (not always true). Isky also made the dimple valve covers for the aftermarket when GM stopped offering the J2.
Hoping someone on the CO forum


has some reference data or items they could compare to determine if these were in fact from the J2 engine or perhaps from the Stude. Here are a couple pics for reference. measuring from the center of the shaft to the center of the adj is 25/32 and to the center of the tip is 1 1/2 if that helps.

 

There isn't a lot of info out there. Using my memory, Gotha used to make the adjustable rocker arms for Oldsmobiles. A quick Google search tells me that company is no longer in business.
What I don't see on your rocker arm is a flat end on the non-adjustable end. I would think it should have a radius to smoothly open the valve.

There used to be a large document on H.A.M.B. about Olds engines that might cover what you want to know. Tony Lombardi (Ross Racing Engines) may know, but he makes his own rocker arm set ups. Charlie Jones and DPL67 on here may also know something.

Report back if you find out anything that would be helpful to others.

 

Thanks for the reply Ralph. The end of the adj. does have a flat radius tip with a witness mark dead center from a valve stem tip. Since these were on a 324 shaft I assume that they must work on a 324. That could be a bad assumption. Who knows the history on these parts that have been setting around forever???
I might send Tony a pic and see what he thinks.

 

Mystery solved. Found an add over on the HAMB for McGurk aftermarket rocker arms that match mine. So these are 1.8 ratio McGurk pieces, Good to know. Hope this helps someone in the future.

 

Thanks for reporting back. I'm surprised McGurk is still around.

 

I don't believe they are but many of their products show up from time to time.