At this point I'm pretty sure I was sold too small of an MC for my disc brake swap on my 67 Coronet. It's 1 1/32", and with 2.75" piston Wilwood GM Metric calipers in the front and 15/16" wheel cylinders in the rear, my pedal is long and mushy and I have no ability to lock the front brakes (manual). I had a harder pedal and more power when I was on all-drum.

If I clamp the rear flex line, a good 80% of my pedal travel is just getting the front brakes from rest to loaded against the discs (this is not a bleeding issue, I can't pump up from this). I do have stopping power, but effort vs output really ramps up beyond moderate braking. Nothing happens with the pedal until it's almost parallel with the top of the gas pedal (I have moved the pedal by hand and listened in my garage, that is just the stroke required to take up the front brakes).

I have been trying to figure out what the best size is to step up to. I have a universal/GM-style two-hole master so I can pick from a lot of stuff. How do you determine this?

I can use 1 1/8 from a 70s D-series, or 1 1/4 for an 80s K1500 with regular OE Metric calipers and huge rear drums, etc. I don't think 1 1/16 would be a large enough step up considering how long and squashy my pedal is now.