[Chuck78]

this shouldn't have any relevance on these matters, as my clutch master in place now is the same bore as the original was, but...I modified my system to use a 67 Chevy 1-ton dual circuit brake master cylinder (bore size chosen in anticipation of front disc brake swap for 1991 Suburban front end, just need to remove residual valve for front circuit when swapping to disc), and then use a single circuit brake master cylinder off of a mechanical linkage clutch Chevy of our era, dismantled and residual valve at the end of the spring in the front removed. This was to get rid of the single master cylinder unit for both clutch and brakes, and add a dual circuit brake system for safety, as well as adding a power booster on a custom bracket & linkage that I made to space it in front of the clutch master.

I do definitely recall that a dozen years ago when I did these modifications, that I did purchase a brake master cylinder for clutch master cylinder conversion use, that was the same bore size as the original combo master cylinder's clutch bore...


EDIT - I can't find my darn factory service manual right now, otherwise I might have a chance of answering this question tonight!!!!!