Midlength question
and yes... I am headed for the best almighty dyno number. (personal number) My MACs with stock Z28 cats welded in the MAC Y-pipe (DO NOT use MAC cats) made 18-20rwhp out of the box. I didn't get to dyno them after cleaning up the flashing, nor doing the "collector mod", but I would project a solid 22-24rwhp.
I went to coated Hooker LTs as I was going heads/cam/nitrous and wanted the extra scavenging as well as the low-end torque. That is where LTs shine over mids...down low. Peak power is comparable, but not torque. Now that you have cheap LTs like Pacesetter, MACs have fallen by the wayside...
I don't have any direct dyno comparisons as the heads/cam were done at the same time as the LTs...
If you can find a set of inexpensive new/used MACs, they are a good-fitting, easily installed header that makes decent power. I sold my set-up for dirt-cheap...
and yes... I am headed for the best almighty dyno number. (personal number)

used the wire machine to weld in small segments of "special street legal cat tubing"