Howdy Asmart:
I'm assuming that you're talking about stock type stuff on a USA log head. anyway the answer is "yes". We are somewhat limited because of the small diameter valve stem of 5/16" on our engines. The smaller diameter does help flow some. And lighter is better for several reasons and especially on the valve side of the rocker, because of the added ratio of the rocker. So anything you can do to lighten springs, retainers, keepers, and valves will have a greater effect than lifter, pushrods and rockers. Less weight in the valve train; requires less valve spring tension to control, less spring tension = less wear, revs faster
Retainers-
OEM stock two piece, 200/250 -30 grams
Old 260 V8, Pre '62 -26 grams
New 260 V8, -24.5 grams
4.0 V6 -23.5 grams.
The part number for the 4.0 V6 one piece retainers is E6TZ-6A536-A. All years and applications for the 4.0 engine used this code. The price was $2.73 each. OUCH!!
Back cutting intake valves slightly lightens the head of the valve and gives the effect of a higher lift cam.
Roller tipped, alloy rockers are available from several sources, but you'd better bring your banker. I have never seen a weight comparison between stock non-adjustible, adjustible, roller tipped and full roller rockers. I can tell you that the total assemble weight of OEM non-adjustible rockers is 7.11 lb. That includes the rockers, separator springs, shaft, staunchons and pushrods. The same assembly with adjustible rockers weighs 7.72 lbs.
The difference is in the adjuster side of the rocker. Personally, I think the additional weight on the pushrod side is worth it for adjustibility.
AzCoupe is working with one of the speciality cam companies to put together a coordinated valve train kit specifically for our engines. So check his website often.
Adios, David