"The only thing is, building a Xizang look-alike, but with a longer wheelbase (for a guy who's going on 20 years older now), with lugs for both disc and V-brakes and maybe for racks and fenders (as in touring bike use as an option)."
Don't know this bike, but if you are a little older etc... Could you just go with steel? Save money, trade the mystical properties of steel for the mystical properties of Ti. Also modern steel, isn't your granddad's steel any more... OK, maybe it is... You would still be getting your own design etc...