[Radioroslyn]

There's a couple of different ways to do it. One is drag a pin down over the winding and count the number of clicks. This will equal the number of turns.
Another is to unwind it and measure the length. Cut a replacement piece of wire the same length and wind it on.
Measure the width of the winding and wind a replace winding to the same width.
The fortunate thing is that it's not part of the tuned circuit so it's not super critical. It's there to transfer the rf signal from plate of the former stage to the grid of the next, supply the hv to the plate, and help match the plate load resistance.

It wouldn't be a bad idea to replace the celluloid strip under the winding and replace it with a strip of modern plastic. Somewhere around there's drawing w/measurements of it.

I would use 38Ga wire.