I'm sure at least half of you are more familiar with cams that I am... so, you've probably already know about the Z/28 cam, that there were more than one, was a surprise to me. The one I just learned of is the "Z/28 Off Road Special" also known as the 140

designed for solid lifter above 3500 rpm, to 7k

First Design Off-Road cam, P/N 3927140 
Casting #3927141 
Intake 257 duration @ .050" (333 advertised)
 Exh. 269 duration @ .050" (346 advertised) 
Lift: .493" intake, .512" exhaust 
Intake Max lift @ 108 deg. ATDC
 Exhaust Max lift @ 116 deg. BTDC

 2nd Design Off-Road cam, P/N 3965754
 Casting #3965751
 Intake 248 duration (324 advertised)
 Exh. 267 duration (334 advertised)
 Lift: .512" intake, .535" exhaust

https://nastyz28.com/threads/gm-140-off-road-cam.226706/
https://www.jalopyjournal.com/forum/threads/z-28-cam-the-140-cam.563684/

this is the clamshell cam I was talking about, Mike