you do not have to use the front mount in order to use the standard trans, the side mounts work fine - either will work with the 3spd, but you already have the side mounts, so easier
as for abuse, unless you like to snap the clutch at full throttle, the original 3spd will hold up fine, but a later [68+] 3spd will have a syncro first [and a different spline count on the output, takes finer toothed yoke]
Bill
