The second rifle I ever owned was a Lithgow SMLE Mk. III* that I bought for $10 at Academy Surplus in Austin, Texas around 1962. When the forend split because of recoil, I decided to sporterize it. I had the gunsmith at McBride's cut back and crown the barrel, remove the rear sight and fill the holes, give the whole thing a high polish blue, and install a ramp front sight and Lyman receiver rear sight. Then I installed and finished a Fajen sporter stock myself. Needless to say this cost a fair amount of money, but I ended up with a very nice-looking sporter. I sold it ten years later for $60 (obviously at a loss).
If this sounds like your situation, I would forget about trying to reconvert it to the military configuration. It would be cheaper just to get an unaltered one.