I like your bikes a lot and an MC1 Adroit in 20" or 21" is also on my list for sure being the last of the KLEIN MTBs I have not yet owned. Let me know if there is one around to be sold.
I think that the most of us agree that those bikes are a work of art and that they need to be preserved. However, preserving such a piece of history comes with certain obligations. Creating a light bike with today's parts is not so difficult - just carry a bunch of Dollars to your LBS and buy whatever is light and expensive; carbon seat post, carbon rims, carbon steerer, carbon seat, 1x12 drive train, modern v-brakes, you name it. Once installed you will have a damn lite bike and you know what: with the right parts installed, it will also ride way better than the ones back in the days. But is that desirable? Where is the difference to a modern carbon bike painted just like your favorite KLEIN from the 90s? Neither is the real thing!
It is a lot more difficult to build a sub 7 Kilo bike with period correct components. Those need to be hunted - you cannot just go to the LBS and buy them. Also, just because PAUL used to be around in the 90s, it does not make mounting today's Love Levers or shifter perches period correct.
These things really do not feel right to me. You have the most desirable frames from the 90s and you try to build something tasteful and extraordinary but in my eyes using parts that are not parts which could have been mounted to that frame in the 90s because they did not exist makes you come way short of what could be achieved if the parts were consistent with the style (and age) and rarity those frames resemble.
One of my classic bikes is also equipped with modern parts for the daily use and there is a certain thrill to just use the best from the past together with today's technologies. This works very good but that does not make the build something special. It is like a Bugatti with an original frame from the 1920s but with an electric conversion. I love Bugattis and I am also quite intrigued by the performance of modern electric cars but it would not be the real thing! It is so much more difficult but desirable to keep a 1920s car running with the technology of its time by also using the parts and materials of that time in particular if it s something as rare and unique as a Bugatti - this is history alive.
I am with you on all things subject to wear like brake pads and tires - use modern parts if the bike is driven but that's an easy swap when you need it for display only.
Other than that guys, go for the hunt! Look for (I am just making this up for illustration purposes) the proper 1st gen. Love Levers with the early style round PAUL logo sticker, look for the proper shifter perches from Grafton as well as maybe the front and rear derailleurs from Precision Billet, etc. If you want to get really light then get inspired by what Klein itself did with its ultra-light versions (hi-e hubs, etc.). You will not get as light as you could with modern parts but once completed, you will be far more satisfied because you have the REAL THING - trust me!
Other than that, do what you want because it is your bike. If you get happy with it they way it is - all is good.
I am keeping attention because I think I have seen some things pointing into the right direction and I really hope you guys do not get me wrong on what I wrote above.
Cheers,
Andy