An SMLE rifle comes in three types: SMLE Mk III - 1132mm / 44.57" SMLE No. 4 Mk 1 - 1129mm / 44.45" SMLE No. 5 "Jungle Carbine" - 1003mm / 39.49"
Entire books have been written on the SMLE. Try your local library or do a web search.
Moderately scarce. The SMLE 1 was produced 1904-1926, making yours a first year production rifle- but they did make a lot of them.
SMLE- aka the Lee Enfield
303 was the .303 inch diameter bullet that was fired by the Short Magazine Lee Enfield- or SMLE. Standard rifle of the British military from 1907 to the1960s, and still in limited use today.
In appearance, these will look like a SMLE, or #1 Mk 3 rifle- since they were made from the SMLE. Visible differences are a larger diameter barrel, and a block of wood that filled the magazine port (and no magazine- they were single shot). Link at the bottom of the page should take you to a photo of a SMLE converted to .410 for prison guard duty.
Value of ANY gun is based on exact make, model, condition. If your Lithgow SMLE is original and correct, depending on condition it can be worth from $500-$1000.
A sporterised Lithgow .303 SMLE
Google the phrase and you will get hundreds of hits.
Bren gun, Lewis gun, SMLE rifle
50-160 USD
Using blueprints.