My '71 P-13 was originally spec'ed for 700c tubulars. I bought it as a frameset with other plans.

Since I had several nice set of 27" wheels I wanted to use them. Just barely was I able to mount them with 27 X 1 & 1/4 Panaracers. The clearances between the tire and the seat tube is a few mm. About the same on the chainstays at the BB.

The good news is the Campagnolo Record calipers fit very nicely.

27" wheels would never fit on my '83. Not even with the 7/8 inch wide tires.