Vic, if you look at the original Vincent steering head it is 1.25" (31.75 mm) at the bottom, where the lower bearing fits, and then the tube is 1.125" (25.875 mm ) all the way up to, and including, the top nut. When I designed the new system for CNC machining I designed the bottom to be the same 1.25" where it fits into the lower block, through the washer FF36 and the bearing and then has a slow taper (no stress concentration points) over more than one inch down to the 1.125" diameter which then continues to the top. My idea for the new dimensions was that the lower part where it is an interference fit into the lower block and where it passes through the washer FF36, would stay the same as original, 1.25", and then would reduce the diameter down to 30 mm all the way up to where the nut is. The tube would then reduce to the correct diameter for the nut, 1.125". That way the same size taper roller bearing could be used top and bottom with no shims etc. [ I have to measure the inside of the top FF1] to see what OD is needed there. I note that the bearing you used is12 mm deep so how did that compare with the original total depth of the cup, cone and balls? It is possible that there are some advantages with your system and I will have to think about it for a while. Remember that we are making a new part so that there is no problem designing to fit a new size of bearing. It is the OD and depth which are potential sources of trouble. I can see that there would be some savings in both time and money to keep the top cup and cone bearing if it is in good condition but I really do not like having to be so careful to capture all the grease covered balls when working with the original bearings. Plus they cost about six times the cost of the taper rollers.