DGULL < I recently resurrected a '88 DB Apex Rigid frame Mtn Bike. I took it from a 7-spd triple to 10-spd triple with the following components that sound very similar to what you're doing;

SHIMANO Deore LX RD-T661 MTB Bicycle 9-speed Rear Derailleur SGS
SRAM PG 1050 10 speed cassette 12-32 PG1050 12/32
Shimano Ultegra CN-6701 10 Speed Super Narrow Road Bike Chain

Shimano Deore M590 9 Speed Triple Chainset 175mm 48.36.26 (BB included)
Shimano 105 5703 Triple STI Shifter
Shimano 105 5703 Triple 10sp Band On Front Mech
Mavic XM 317 Wheelset 26" MTB Rim Shimano Deore Hub

Origin8 Stem MTB Quill Adapter 22.2/28.6 Black
FSA Gossamer New Ergo Road Handlebars, 31.8, 44cm

The only issue that I haven't yet fully worked out is the FD is a little picky about getting into the inner 26t ring.

Pictures posting as soon as the rain stops...