Wow, didn't know they were that flexy those years! I'll have to take a closer look at one next time I see. I was actually going to use the later rear crossmember at the tail of the bed on my 77 as I figured the holes would create some additional access that I could have used.
It just depends on the usage of the truck. Especially at the rear, the later crossmember with holes in it will be fine for most trucks. But I'm working toward my truck being a Pro-Touring/Auto-X build, so I need the stiffness. I'll also be replacing my rear crossmember with a TinWorks fab unit that is stiffer
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But the '81-up 2wd crossmembers have so much material cut out of them, even a street truck/cruiser could benefit from a stouter version. I've seen a handful of guys swap in the 4wd one since it's solid. Here's a pic of mine, note the huge holes and that where it rivets to the frame has legs cuz there's more material taken out of the sides. That was part of the weight reduction they did for '81-up, I think they saved 300lbs or so over an '80-down truck.
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