Go for it. ..... It is could 303 Sporting in France, I have a No4 and a MkII in it. It is a very nice round to shoot.
Cut one turn of the barrel mounting thread. Which is about 2.65mm, and re cut the extractor grove, just as the bindi2 said.
Cut the same length off the bottom of a 303 btit die for reloading. Use the die the full length re size after you have anealed fired cases but not necessary with new.
the reloading problems you would have with the 303 brit will be the same i.e crushed shoulders.
Use a lighter bullet, about a 150 grain.
Learn Frenchicon and there is plenty info on the WWW.