Here's Sheldon's take on the existence of 27" tubulars, along with other bits of info regarding tubular sizing. Are you sure about the rims being 27" instead of 700c?

"Standard size tubular tires use a rim that corresponds in diameter to a 622 mm (700C) clincher rim.

Back in the 1970s, 622 mm clinchers were very rare in the U.S., and most sporty bikes used either 630 mm (27 inch) clinchers, or standard (622 mm) tubulars.

The fact that these sizes are so close led to an in-accurate habit of referring to "27 inch" tubulars. This careless nomenclature still causes confusion, and people often imagine that there is a different "27 inch" size in tubulars as there is in clinchers.

This is not true. THERE IS ACTUALLY NO SUCH THING AS A "27 INCH" TUBULAR.

All full-size tubulars fit all full-size tubular rims.

There are smaller tubulars, "26 inch", "24 inch" and even smaller, but those are VERY uncommon, mainly used for children's race bikes, which hardly exist at all in the U.S. The smaller sizes are very poorly standardized; tires and rims of nominally the same size may not fit one another."