Trek 8000 with Ultegra Rear

[Dominican boy]

My Trek 8000 cannot be sitting anymore in the basement

1 Frame 19.5
1 Rear derailleur Ultegra medium
1 Truvativ Stylo Crankset (Triple Crankset)
1 Cassette from Ultegra 12-something road(looks small) 9 speed
1 11-34 Sram Cassete 9 speed
Front Derailleur XT

I plan to build a MTB training bike for pavement. can i put a Triple Crankset with the Ultegra Rear?

Can i take the granny gear and do 2 chainring with the Ultegra rear?

Any comments would be appreciated

[mdesorcie]

Your choice of shifters will go a long way in determining what you can use. My experience is that STI shifters will only work with road gear all around - they are very finicky. If you are planning on MTB shift/brakes, you can use either cassette, but you will probably need a Deore (or similar) rear derailleur. It has to do with the angles/size of the derailleur cage - the shifters are designed to throw the derailleur "X" amount. I would basically figure out shifter choice (along with drop or flat bar) and let that determine which part to buy.