Master cylinder for Front disc brakes on 67 Barracuda

The disc MC always has a wire bale top (never a bolt); it has one large compartment and one small compartment; it has one round end and one square end (although, oddly, sometimes the square end is the front and sometimes it's the back — I have cores of both types). Piston diameter could be 15/16, 1" or 1-1/32" — as JYH says, check it if it matters to you. Bigger is firmer (but counterintuitively, power brakes got the smaller bores when there was a difference — it was a function of leverage).