I removed the clutch and brake master cylinders a while ago and had the same issues getting the clevis pins out as already mentioned numerous times by others. One of the pins had decided to "weld" itself to the push-rod so took a lot of penetrating oil and persuasion to extract. This was not surprising as the car last turned a wheel in anger 28 years ago.
Once the master cylinders were unbolted I found in the cubby hole the felt mat that BMC installed to soak up any fluid drips from the master cylinders (part HYB1319), plus a well-worn old clevis pin that had obviously been hiding there since removed by the previous owner many decades ago.
Attachment:
HYB1319 Felt Pad Brake Clutch.jpg
Attachment:
HYB1258 Installation Felt Strip YDO4 5 6 7 wm.jpg