My 273 turned out to be a 318...what did I buy?

@Professor Fate. is right on the money with a swap to a dual pot master cylinder. Highly recommend doing it for safety sake. Here's when I did mine in a 66. I now have headers so there is a little more space.
Second, the master cylinder. The originals are a single-reservoir design which was superseded by a dual-reservoir design in '67.
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