Square taper makes it a bit less predictable since it's always hard to know how far they suck down on the square spindles.
When you say they don't have enough clearance on the ND side, do they touch or are they just close? What's the spacing difference between the drive side and non-drive side?
Also, which Square Taper BB do you have? Is it one that allows a fully adjustable chainline with no e-type flange on the drive side, or does it have the flange? Is it the correct size for a 73mm BB shell?
And a better choice for the front derailleur will be the SLX dual ring model as the cage is smaller and will give you more tire and swingarm clearance.
It is the correct shell and yes it has the flange on the drive side, Shimano XT. The nd crank is close but does not touch. You can tell if the frame and or the crank flexed, it would touch. My son rides pretty hard and weighs about 190 so this is plausable.
What clearance do you have on the drive side pedal arm? With square taper the spindle length will be added symmetrically, so if you bump up to a 118mm it will add 2.5mm on each side which might become a chainline issue if the distance moves out on the drive side.
I'm about 195-200 pounds and when I had XTR cranks on my SXC with the original swingarm there was about 3mm clearance on each side. The new swingarm I just installed has more clearance so it was less of an issue.
Does your SXC swingarm yoke look like the top picture or bottom picture? If it has the notch for the derailleur clamp and cable clamp clearance you have the most flexibility in derailleur choice. If its like the top one you have fewer options to find a front derailleur that fits without touching the swingarm, a Deore bottom pull will fit, and an XT or SLX will take a lot of fiddling with clamp bolt swaping. The top one is an early 2007 version, the later ones had the notch machined into them. If you bought the frame new from an authorized dealer the swingarm change is apparently covered by warranty.
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