I'm just about done with mine.....if you're going to go to the lengths of changing out the barrel, etc., there are some other, much more glaring problems with the kit that you have not yet addressed:
1. The location of the pistol port/empty shell port is too high. The locating hull is too high on the turret. Easiest fix is removing the pin on the back of the hatch and the putting the whole thing were it belongs.
2. Weld seams (already mentioned) should be raised. Easiest fix with styrene rod, liquid cement, a hobby knife, and patience.
3. I filled that gap at the bottom right front of the turret. It's supposed to be depicting a later turret with thickened cheek armor, except the CHEEK ISN'T ACTUALLY THICKER ON THE KIT! So you have to thicken it yourself w/putty or fill in that gap.
4. The sandshield skirts molded along the bottom edge of upper hull are horrible! They have molded on bolts (which should only be there if the skirts are fitted!) and a seam running the whole length. I cut mine off, carefully, with a knife and added my own of styrene strip, drilling holes in the appropriate places with a pin vise.
5. The fire extiguishers were actually mounted on a L shaped bracket, not just attached to the hull as depicted in the kit. Styrene strip an easy fix.
That's all I noticed at first glance. Good luck with the rest of it.
Rob