Horseman,
The Number 4, Mark I, is definitely the one you want. But, remember, the peep sights on these were made to hit a man at 100 yard, not a rabbit. So, even on their closest setting, they may shoot 10 to 12 inches high at 100 yards. So, be prepared to have to replace the front sight with a taller one.
I'll leave it to the experts here to advise what the best front sight replacement would be, and where to get one.
Also, DITTO:Stay away from the Jungle Carbines, either original or converted. The muzzle blast and noise is horrendous! (Also, the original Jungle Carbines had special "cuts" in the recievers to make them lighter, called lightering cuts. Unfortunately, these made the receivers too springy, and gave rise to the problem of the "wandering zero". I.e., no matter how many times you sighted it in, the point of zero would wander. The Jungle Carbines were introduced at the very end of WWII, and the complaints started pouring in, and I think their production ceased very soon afterwards.)
Best Regards, Mannyrock