The Wright R-1750 engine didn't have sodium filled valves from the onset, it was when it was developed to 1823 cubic inches during the "F" model stage in the mid-1930's, that it received Heron's valves.
The P&W R-2800 was in development during this time, so going from memory, I couldn't recall which engine got the sodium valves first.
Heron applied for the patent around the mid-20's, a few years after he moved to the U.S. from Britain, but I believe it was several years before his patent was approved and he perfected the process. So the valves would have been available to manufacturers by the early/mid 1930's.
By the way, Heron also developed the improved cylinder for the radial and was also the grandfather of high-octane fuel - brilliant guy.