Master Cylinder for KH Brakes

I just got a new master cylinder from Rock Auto (Dorman pn M75817). The entry specified the Kelsey Hayes disk brakes, which my '72 Swinger has from the factory.

The new MC has different size reservoirs for the front and rear brakes, and the sizes for the brake lines are 1/2" front and 9/16" rear. The master cylinder on the car has equal sized reservoirs, and the brake lines are the same size.

Did I receive the wrong MC, or was the wrong MC on the car from a previous owner? Any help would be appreciated!

vm

..new master is correct

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Did I receive the wrong MC, or was the wrong MC on the car from a previous owner?

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(1) no, you're good now (2) my guess yes a drum/drum M/C (equal size reservoirs) & if it had no RPV in the disc half next to the firewall (& you'd know it if it did) no prob as long as it was kept topped off as that reservoir half was larger for the discs app (calipers use more fluid vol). We (& your prior owner) keep our stuff topped off whereas Grandpa may not & lawsuit prevention is paramount.