Sounds like you should wait and see what you get then. 27" is likely but it could go either way. Schrader valves on their own don't necessarily mean anything. You can always put presta tubes back in. There's a simple adapter grommet. Even that isn't strictly needed.

In the 70s it was common to replace sew ups with 27" rims because that was the dominant size then, and tires and rims were easily available. 700c clinchers are the same size as sew up rims, but initially they were sort of a niche market size for racers than wanted to train on clinchers and not readjust their brakes. (you may know that already)