"The Eidolon must have limbs for the synthesis to cast spells with somatic components"
Note it just says limbs it does not say limbs(arms) therefore any limb evolution would work including legs.
Poor thread, please follow me.
Remember also that the summoner is wearing the eidolon like a biological, all-encompassing "suit," and the eidolon's shape limits what the summoner can do. If the eidolon doesn't have arms, the summoner can't use his own arms to manipulate objects, make attacks, cast somatic spells, or anything else requiring arms--while fused, the summoner's limbs are trapped within the armless eidolon-suit, and he isn't able to use them to manipulate things. The summoner isn't able to extend his own body parts outside of the eidolon-suit; if he wants to be able to manipulate things with arms, the eidolon needs arms (though tentacles are sufficient for simple tasks).
This thread needs to be moved to its rightful place in the afterlife.
Also: if the target is willing, the touch spell is delivered automatically, without a to-hit roll. I.e., a magus can deliver touch spells to friendly targets as a part of spell combat. That spell can be delivered via the magus' weapon.
Normally I would only do this with a whip, to deliver a critical buff or heal, but if my opponent is willing ...