I did something similar years ago when I converted my 69 Camaro to front disks. I did not initially use a MC for disk brakes. It stopped OK, a little better than drums, but not what I expected disks to do. The original MC went south so I opted for a Corvette MC with front disks and rear drums, along with the proper proportioning valving. The difference was night and day, all of a sudden my Camaro had vastly improved braking.