Looks to me to be a Mk1.
Per original posters question:
For target competition, range toy, or collectors purposes, get the P14/17.
For combat/battle rifle, give me the #4Mk1/2. With stripper clips, and practice, you can lay down some ferocious fire with a Mk4.
Mine is a '43 Fazerkerly, with the machined vernier sight, "F" stamped but I put it on the rifle. Had a L-two aperture rear sight after a post war rebuild. It has a near new barrel, and is VERY accurate. (~2moa).
At a recent vintage military rifle match (bolt action only) I wore out the competition. Several Swiss and '03's, but if you don't get the rounds off into the scoring rings, it doesn't matter HOW ACCURATE your rifle is. 10rds in the black for a 92, beats 2 zero's for a 88!
Re: the long chambers. Less for "crud tolerance" than for mitigating high pressures from tropical heat, or heated firearm from high rate of fire.
Note how the .17HMR rim fire is designed to blow the neck foward to reduce initial chamber pressures, and ease bolt opening resistance.