Slant 6 rocker arm metalurgy

Is there any information available on what kind of metal makes up the main body of the rocker arms on a mechanical-lifter slant 6 engine?

I need to know whether that main '6 rocker arm body is a type of steel that can be welded on, and how hard it is, in terms of its ability to be machined.

Has anybody ever done any research on this?

Any information will be appreciated.:cheers:

Bill