#208 (4-4-0) was a D16b, later superheated, starting in 1914 and re-classed D16sb.
It was built by the Pennsy's Juniata Shops in 1905-06 (I don't have my roster in front of me at the moment, but it was NOT prior to 1905.)
The number plates were round, as were ALL Pennsy number plates at that time.
Keystone number plates came later, and were only used on passenger locomotives. Photos of Pennsy engines in the 1940s showed round plates on their freight engines.
The LIRR adopted the Pennsy-style Keystone number plates on their passsenger locomotives starting in the Fall of 1942.
The D16's were all retired by 1931.
Here's a distant shot of one westbound at Patchogue around 1908. The round number plate is visible (but no "PD" tower yet):
And here's a closeup of #201's plate, visible behind the LIRR's Trainmen's Trio taken at Morris Park Shops in 1924:
Dave Keller