Hey, beautiful MXZ! blah blah blah
Thank you for the kind words, Hope to see yours here soon
When I bought this bike I had the same problem, there was no routing system and no way to mount one the previous owner had muddled together a dodgy system but since there was a cable stop near the B/B area I knew there had to be another way, My solution was ( once new paint had been applied ) to get a B/B shimano cable router = http://www.sjscycles.com/store/6499shimanosmsp17msmall.gif
and squash it a little using a G-clamp until it was the right size for the B/B shell and then simply super-glue into place , Sure its not how they did it, but it works....
The original way was to use the steel plate you describe with the long bolts, set up was a bit like the old onza HO cantis - usually trial & error . if you dont have the parts anymore your best bet is to manufacture some yourself by drilling a small hole in large enough (& thick enough) washer, best to ask a competent DIY'er with the correct tools, but if your sticking to cantilever brakes you can still pick some onza HO's cheapish, they will work without em.
Never actually weighed the frame, I was to eager to build her up, Kestrel could'nt tell me anything about them either (too far back) .
By the way if you want decals try http://www.yellowjersey.org/ksdecal.html
get me a set while you are there
Stabled = 91 Browning Test unit - Trimble Double U - kestrel MXZ Black - 87 Chas Roberts Snow Leopard - 88 Overbury's pioneer - Dave Yates Diabolo - Proflex RF-1 team replica - Mk1 Thorn Nomad - Dave hinde disc - frontiera 531 - Serotta Proflex