It's been years since I've heard of aluminum retainers. But I'm willing to bet that either build with the 4.10s and a four speed had explosive mid range power. RIP, Crane Cams. I wish we could buy parts of that quality again.
Yes they were so very light it was like the difference between a quarter and a dime with chromoly. Kind of sketchy I guess but I will tell you that thing would wind.