Yes. You CAN use a MTB crankset on a Road bike's frame ...
- you may want to replace what is probably a 42t outer chainring with either a 46t or 48t outer chainring, BTW.
FWIW. I recommend a
113mm Shimano Octalink + LX-or-XT crank OR a
109.5mm Shimano Octalink + XTR crank ... you'll find these on eBay ...
- the spline pattern on the two TYPES of Octalink BBs differ & are not interchangeable
There may certainly be OTHER crankset & BB combinations which will work BUT you may have to worry about the chainrings being too far outboard from the bike's centerline.
BTW. OLDER, square-taper 110BCD cranksets usually have mounts for a Granny -- I think the BB length is 118mm, but a shorter spindle can often be used ... the
caveat is that you need to know if the crank uses a symmetrical or asymmetrical spindle ...
I know someone who uses a 22t (?!?) with a "standard" 130BCD Road crank (DA 7700, Octalink) ... BUT, he uses a 39t
Triplizer MIDDLE chainring (~$80+) to preclude (¿?) any chance of the chain becoming lodged when making the transition from the inner to middle chainring. He used a 118mm Octalink BB, but I found that the 112.5mm (XTR) Octalink BB could be used with Triple cranksets.
THE OTHER OPTION is to simply use a MTB rear derailleur + MTB Cassette ... even with a Triple Road crankset if you think you need it.
Just be sure that the 8-speed Shimano Cassette is of a reasonably recent vintage and that the cogs are ramped ... otherwise, just get a new SRAM 8-speed Cassette.
BTW, if the front shifter is a Road shifter designed for an 8-speed drivetrain then the front derailleur needs to be designated for an 8-speed Road drivetrain ... your current front derailleur may be "okay."
