The difference in cubic inches between the 15/16" and 1" bore is pretty small. A jump from 1" to 1 1/8" is pretty substantial and to 1 1/4 is BIG.
Only Trucks and vans have MC's that large a bore and usually have a big vaccumn booster.
If your current master cyl is 1 1/8" bore, AND has the deep hole required for a manual pushrod, you could try that on a manual system using the top hole in your brake pedal.
I'm assuming your brake pedal has the upper pushrod hole like the Camaro does.
The added weight of your car over a camaro will probably make your larger brakes act like stock brakes on a Camaro.
I kinda doubt you will be happy with manual brakes on your car. People I have heard from that like their manual brakes are pretty big guys with small block engines.
I'm in a quandry over this too, as I would like to dump my booster and put manual brakes on my Camaro.
A power brake system rarely needs over 50 lbs pedal pressure to lock the front wheels.
With a manual brake system, I think you will be in the 90 lb range, maybe a little higher, depending on car weight.
About the pads, I have a friend with a mid 70's vette with manual brakes, he bought a booster and MC to go Power brake on it.
He put new Perf Friction pads on it and his brake pedal effort declined enough that he sold his booster and is staying with manual discs. I think it is only a change from .3 to .4 coefficient of friction of the pads but that makes enough difference.
I don't know what the pads are, I think carbon Metallic, I don't think they are any harder on rotors than stock pads, probably easier on them.
The rear calipers may be too small a piston size. I don't know what they are offhand but I remember my old 85 Z/28 had fairly small pistons in the rear. If the rotor is small too, that's a double whammy. Look for a larger dia rear rotor that may swap with some mods to move the caliper mount out to compensate.
Check my web page for First Gen Camaro suspension info:
David's Motorsports page
First Gen Suspension Page
67 RS 327
69 Camaro Vintage Racer
65 Lola T-70 Chev 350 Can-Am Vintage Racer