I agree with the comments on the wheels, when building my Litespeed, Mavic 230SPB were the lightest rims without spending really silly money at the time. I had them professionally built with Hope ti hubs, DT revolution stainless butted spokes, annodised nipples and matching Hope skewers.
Other kit fitted were a Flite Ti saddle, Raceface XY seatpost, Raceface top end bottom bracket, Raceface Deus XC stem and Raceface Turbine forged cranks and chainrings. Just those few top end items cost me approx. £570 way back in 1998!
Then I added xtr 8speed rear mech, xtr v-brakes, XTR Spuds, xt shifters, xt front mech, xt cassette, top end sram slotted chain, xt cables, double butted lightweight alloy xc bars.
The 3.5lb 18" Litespeed Ti frame was fitted with a Hope headset and Pace RC31 carbon rigid forks.
My only 'extravagance' is a Ringle cage, carbon bar ends, yeti grips and Conti 520g tyres. These last items I could do without, but would make riding a problem. 350g tyres tend to puncture every time, which is not worth it. I use Air Bs which are fine though with good tyres.
...........all adds up to an honest 20.5lb. I have seen others on Retrobike claim weight as low as 18.7lb with a steel frame, but I can't see how this is honestly possible. I have even asked for tips, but I get no answer.
Good luck and I am looking forward to the final weigh-in as I feel every bike enthusiast has to have a go at a light weight project at least once to get it out of their system!
p.s. when you do get it finally built, nothing can prepare you for just how fast it accelerates and climbs to a 'normal' mountain bike and its worth all the effort and cost for the sheer 'grin' factor a superbike gives you!
1998 Kona 853 Explosif, 1999 NOS Kona 853 Explosif, 1999 NOS Lynskey signed Litespeed Obed Ti, 1999 Marin Mount Vision (custom), Cannondale Bad Boy 700c Disc (everyday hack) and a 1993 Marin for the Wife. Latest build in progress is a 1993 Marin Eldridge Grade with original paint.
"Pain is temporary. It may last a minute, or an hour, or a day, but eventually it will subside and something else will take its place. If I quit, however, it lasts forever."