"Remington Lee was manufactured in 45-70, 30-40 Krag, 43 Spanish, 6mm Navy Special, 30, 45, 50, 42 CF, 303 British and 11mm" - source "Eugene Myszkowski - The Remington Lee Rifle published 1994". There is a Remington lee in 303 British on display in the Remington Arms Co, Museum in Ilion, NY.
I suggest posting a picture of the magazine you're after....some interesting stuff is tucked away...never know what will surface.
Any body got a Remington Lee Receiver or a rifle in poor condition they what to part with?