I would only use a Mk. IV, No. 1 in excellent condition for re-barreling to a different cartridge. Here in Canada, guys are currently converting these to .45-70s and there are several other rounds that work. The action can handle rimless cases, there were a number of very fine sniper rifles made at the old Longbranch Arsenal here in Canada during the '50s and '60s, these were then used in target competition at Bisley, in England. I wouldn't bother doing this as it is cost prohibitive, however, the East Indians also made .308s at their arsenal and these are easily found. The quality is about what you might expect from India, at least the few I have examined.
You might want to check into the .303/.375 Axite cartridge, this MIGHT be the best way to go; get an older "Cartridges of the World" and you will find the data for it therein. Frankly, I have owned a minty Jungle Carbine, a Parker-Hale sporter from the early '60s when their quality was excellent and a minty sporter made by Geo. Gibbs & Son of Bristol, in "Merry England"; I wouldn't give you one old Mod. 70 (of which I have quite a few) or good Mauser (lots of those,too) for several shiploads of SMLEs, of any type.
A .338-303 wildcat using .338-.308 wildcat data is easy to make and should give you a good Deer round with a 225 gr. bullet; that is the way I would go, if I were not cured forever of any desire for "Smellies".