To be clear ... the metal work required is 95% finishing ... not fitting.
Fitting - Like with the brass buttplate on the Colonial rifle, there is a bit of fitting of the dovetail feature (forms the slide for the patchbox lid) and spring lock piece (that holds the lid shut). But, Jim's online videos show this all in detail. If you are OK handy with hand tools, and watch his videos once or twice all the way through - you'll get it. Your 1st viewing gives you the scope of what you're trying to accomplish, then you'll absorb minute details for specific points when watched again. There is a little fitting to seat the muzzle cap, but is also extremely well shown in his YouTube videos.
Finishing - The brass parts need to be filed and sanded (metal paper) to your degree of desired finish. Same with the steel on the lock. Again, all VERY WELL explained in Jim's online videos. To me, the brass finishing was the worst part of the job; it's not hard, just tedious ... I now HATE finishing brass! You will need to draw file the steel barrel and I can tell you it is WELL WORTH IT to buy the $10 to $12 Bahco brand file he recommends, that can be bought on Amazon. I thought that I had good files for draw filing on hand, but let me tell you ... a new Bahco one filed a flat in one 5th of the time using mine! They are amazing files and about 4 of my friends bought them just based on my observations alone!
For a simple metal finish, use cold blue on a clean barrel and rub it back to be a dark or light gray using fine ScotchBrite - whatever suits your fancy.
To be honest - his locks are superior - a completed Kibler is 2-3X the 'quality' of a factory longrifle! And you really can't mess it up as long as you thoroughly read through his instructions before starting, then follow along with his instructions/videos and go at YOUR pace. PM me for assistance or even contact Jim directly. He even actively responds to build posts and/or questions over on another MZL'ing Forum, but I won't post that link here out of respect for this fine Site.
Inletting - On the Colonial build I had, it was mostly using a SHARP 1/4" wide chisel to form a true square corner where needed on the inlets, like at the end of the breech plug tang or trigger plate, as his CNC cutting tool only forms a 1/32" radius. As a former GE Aircraft Engines-trained machinist (a true machinist, not just that of a CNC push button operator) I remain EXTREMELY impressed with the degree of precision that Jim Kibler has achieved on a wood product!