are you planning on riding it regularly? i run mine at gap creek often, i have Judy XC with speed springs and a non leaking cartridge...suspect its a risse. anyhow...the forks work really well, given their age, and are easy to look after. Mag 21 would look great....but they dont work nearly as well, and are pretty flexy. SID are too new i think
M737 cantilevers on mine, with some new BBB pads, set up properly they work just fine i think. the rear brake on a Zaskar does suffer from only having the one cable stop near the front, and the rest is guided. if you ran V brakes, i would think you may have to run a full outer cable, and zip tie it to the frame....possibly not nice. you would get powerful brakes though..
i reckon you should stick some 1993 decals on it also, they are one of the best looking of the GT All Terra downtube series i think...nice and simple, just the GT yellow and the black vinyl. classic.