>>1935306>Stil. road bikes are so cheap used it may be just better to get one of those with MUCH lighter components and as you said get a different frame or bike for mtb.I'm after a drop bar project that can work on road or offroad (aka """gravel"""). I really like "vintage" Shimano stuff, I put these beautiful Ultegra crankarms from around 2006 on my Brompton.
I'll hunt around, the sweetspot would be something about 10 years old that has hydraulic Shimano calipers but with external cable routing. This video is really cool, but v-brakes are a no-no for off-road:
https://www.youtube.com/watch?v=JaDPVh17QeEThe frame alone, plus the Ultegra / Dura ace parts would be WAY more if bought separately than the £500 he paid, and they're just as good as anything made today.