An aircraft museum in the USA sent a request to make 20 leftside and 20 rightside rocker cover gaskets for a Rolls Royce Merlin 1590V Mk35 engine. They sent some old gaskets along with a pattern for some changes to the outside of the gaskets. We offered three material choices along with spec sheets and the customer chose to have these die-cut using a material known as S-207 from Interface Solutions. The rocker cover gaskets differ just slightly between left and right, so we marked them accordingly as shown below the image of one of the bunches of gaskets.
Rocker Cover Gaskets (20)
Gaskets marked for left/right
Here is an image of a Rolls Royce Merlin engine:
Wikipedia has full details on these engines here:
The Gaskets-to-Go Custom Gaskets Blog 