Does Master cylinder bore size really make a difference.

i just got my 69 Swinger 340 back on the road after sitting over 20 years, I had a guy go over the 10" brakes and he replaced everything including the master cylinder (he also used Dot 5 silicone brake fluid). The brakes always worked great before I parked it and now the pedal is high but the pedal feel is hard and the car doesn't stop well at all. I then took it to another brake specialist and he readjusted the brakes and checked everything out and it stops a little better but the pedal is still hard and if I stand on the pedal as hard as I can the brakes wont lock up. Do you think a smaller master cylinder bore would help? Thanks Joe