[Alan Roehrich]

There are several outlets for the 7/16" small block rockers, even though I have a mill, I'm not sure I'd bother with trying to open a set of 3/8" rockers up to fit.

I would certainly not clamp them in a vise, as you will likely not be able to hold them securely enough. I think I'd take a piece of flat stock and mill slots in it to set the rockers in, and then clamp the flat stock and the rocker to the mill table. You need to put something between the clamp and the rocker to prevent the clamp from scoring the rocker, as the scoring will create stress risers.

Ken is correct, any heat generated by cutting the rockers will ruin the heat treat, it must be carried off by coolant. Are you going to have to drill the rocker balls as well?