I converted a 90s Giant Cypress into a gravel bike. Got rid of the cheap suspension fork, which did almost nothing and replaced it with a super light, rigid aluminum fork—saved a ton of weight. Replaced flat bar with drops and Shimano 8 speed brifters. For the front brakes I used road disc calipers. Started out with 160mm discs but stopping power was pretty mediocre. After switching to 203mm I feel braking is finally acceptable.
For the rears I opted for cantilever brakes because the frame does not have disc mounts. I’ve used v-brakes with Travel Agents previously but I don’t like how the cable gets embedded into the pulley and becomes impossible to adjust later. I’m pretty happy with the cantilever setup.
A few minor issues: it’s hard to find 8 speed cassettes with a good range and most that are available are made for low end bikes. I may switch to 10 speed in the future. I would not even consider Shimano 9 speed as they seem to be the most unreliable.
Thr fork I sourced is for a mountain bike which lifts up the front end quite a bit. That changes the geometry of the bike and I can feel it in the handling too but I also like the more upright position. It’s my most comfortable bike, with 42mm tires at 35 psi.
Having done this though, I think that economically it does not make sense to do a custom build unless you have all of the parts just hanging around. A cheap new gravel bike now starts at around $500.