I have done the same as August Bicycles and never had an issue. I took it a little further & also drilled 4mm holes every 90 degrees in the steer tube either side of the join & welded the sleeve to the steer tube at each of these holes so even if the butt joint failed there is a bit of a fail...
Torsional stiffness is where efficiency stems from, vertical stiffness or lack of is where comfort is.
Sod the UCI, beam/cruciform is where it's at for carbon. Maybe then we can have both (and f'ing huge logos).
Looks to me that all the extra material (external butting) if forward of the chainstay bridge and the sleeve overlap is extremly unlikely to extend through the bent section.
I dont know if it is worth every cent. If you are going to ride it to experience the fabled ride quality that chainsuck damage is a crack waiting to happen.
Also, is that a crease below the bottle cage mount in the second pic?
M/L by the look of it, nasty chain suck damage. Best guess 1993?
https://www.ebay.com/itm/Fat-City-Cycles-Titanium-Fat-Chance-Vintage-MTB-Frame-/396069798356?mkcid=1&mkrid=711-53200-19255-0&siteid=0&customid=link&campid=5338793687&toolid=20001&mkevt=1