Master Cylinder Size

I 3rd a 15/16".

When I replaced the original 1-pot on my 66 Barracuda I went with a 1- 1/8". Yup, it was hard as a rock. Swapped to a 15/16" and bam, just the ticket. I did buy an adjustable pushrod for the first one, but I might be able to go back with the original.