1971 Chevy Camaro brakes

why do you want the wheels to lock up? if you want it to lock up take out the proportioning valves.

if you want it to lock up stand on the pedal when you stop it that will lock them and try going faster.

if it brakes like a normal vehicle dont be trying to mess with it.

Even if I stand on it, like in an emergency, on dirt or sand, the brakes won't stop the wheels, you just slow down, slowly!!!
It's like the calipers aren't squeezing enough, and I need to stop. At 60, I've driven lots of 'normal' , and this ain't it.

with vehicle off try to pump up the brakes and hold about 200 pounds of pressure on the pedal. does pedal stay up or go down?

check the pressure and let me know what your getting. is it a dual split brake system or is it diagonal split like the older model vehicles.

if its diagonal dont be expecting too much of a locking going on.

how slow does it stop?

I think you said it all with "no power assist" the older cars just didn't stop that well...Do you have non-OE tire size? Did you seat in the new pads very slowly and completely? "Avoid panic stops first 200 miles" is one thing I've seen on packages...This seems excessively cautious.
It's always important to seat them in , though.

if you can stand on the pedal and push all your weight with both feet and that wont lock it up there may be a issue.

but if your pushing hard with one foot and non power assist. you aint goign to lock it up.