mvh said

If the two chambers are equal size, it is not a factory disc brake master cylinder, which suggests that the disc brakes were not original. So the bore is kind of irrelevant.

For 1970, the factory disc brake master cylinder bore would have been 1-1/32". The master cylinder would have one large chamber and one small chamber, with a wire bale clamp on the lid.

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slantsixdan said

No, because the car is over half a century old and parts get changed (and as has already been stated, a master cylinder with equal-size reservoirs is not correct for a disc brake system—that's for a drum brake system, and using it with disc brakes can make problems).

The original master cylinder on that car had a ø1" bore. The master cylinder with the ø1-1/32" bore mentioned by mvh came in for 1971. However, the '67-'70 ø1" disc brake master cylinder has grown difficult to buy. There is no reason why you can't use the '71-up ø1-1/32" item; that's this one.

While you are paying attention to the brakes, take easy and inexpensive action to permanently fix the rear-lockup problem the disc-brake A-bodies all had from the factory; info here.

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