Hello  Been trying to buy a new stock Master cylinder. Have bought two that were suppose to fit. Both  sides the vertical mounting holes are spaced to far apart. Need vertical mounting holes 1 7/8" OC. I suspect they were for a 56? car,  probably would work by boring two top hole lower.

vertical holes?  I just pulled the master cylinder off my 57 to do a power brake install and it and the master cylinder on my 58 are both horizontal.

Thanks for reply.  The four mounting holes on MC. two top, two bottom. I have bought 2 MC that were supposed to be to fit. but didnt. The spacing between the two top holes are correct. Spacing between top and bottom holes is not. Need one this is  1 7/8" OC hole spacing. Two that were supposed to fit were 2 3/8 OC. Was a pic I noticed when looking  of one that had 6 holes, evidently  would fit pre 57 cars and 57-59 cars.

IF, you have the old MC, you might want to look into having in sleeved with SS or brass. White Post Restorations comes to mind. I don't recall their location, but a Google search should get you the contact information.
John

Thanks John  found one with right mounting spacing.

post what you found so others will know

Master cylinder that fits MC23222

I seem to recall a dimple in the firewall that was to locate a 2nd hole / spacing. Just curious if you noticed one also, and if it could have been that different hole spacing you were running into with the MCs.
I'm pretty sure it was the hole spacing I needed for my Mustang hydoboost unit.