Do you have enough clutch pedal travel to have the top belt a bit looser? New belts are not as flexible as old belts: it could be applying some tension even with the jockey pulley loose enough to have de-clutched an old belt. If you want to check whether that is the problem, adjust the clutch pull-rod so the belt is looser in the de-clutched position, then see if it disengages properly. If that works, you can re-adjust it back to normal after the new belt is broken in.
If the belt sits just at the top of the pulley, or a little bit lower, it is the right width. There is an alternative V-angle, but I think it is only found in automotive belts. (Using a belt with the wrong V-angle could cause the clutch to stick).
