The Valve spring retainers are aluminum and were made by Offy. I have a set on my 235. Some say aluminum is too soft for retainers and it is tougher to keep the valves adjusted. Could be, I don't know. They are pretty though and as you said, very light. Offy also made an inner valve spring and special pushrods also. I have an old Offy catalog that lists the stuff.
