Who's rockers are these?

yes, the T&D was some Swiss watch looking stuff. Even the roller tip was on it own bearings with a C-clip to service it. Why use stainless rockers..whats the upside? Stainless fasteners are pretty but are not as strong and corrosion control is no an issue under a valve cover... Just wondering....

They use aluminum because it's relatively cheap and very easy to machine.

Most anybody making rockers today is offering rockers in steel of some form.

Aluminum is for Pistons.