Are these two archetypes able to be combined? They both alter the Arcane Pool, but in different ways (SD replaces the weapon buffing ability that BB doesn't need, BB lowers the total Arcana).
By RAW, no they cannot, since they affect the same ability. Even if one of the affects is optional, it's still by RAW considered an overlap.
Speaking personally and into the realm of house rules, I allow it myself, and just say that the choice of that particular level's ability is locked into place by the Spelldancer archetype, rather than giving the optional choice they'd have if they were just Bladebound.