Need help selecting master cylinder

Hey y'all. So previous owner converted the car to 4 wheel discs. Great stuff. Problem is they did this with a power booster, and combined with a pretty nasty cam. She's got maybe 6" vacuum at idle. So power brakes ain't gonna work.

A little searching around suggests a 15/16" bore mc might work as a manual brake setup. Thoughts?

This is the mc I'm thinking about.

Dorman M80266 Dorman Brake Master Cylinders | Summit Racing

I have a 15/16'' master cyl on mine , wish I`d gone w/ a 7/8'' , stops good , but wont lock up at all.
Doesn`t have any abnormal travel at all !