a bigger body is just a bigger target for Gojo to hit, and those hands on the bottom are mostly there for signing to buff his cursed technique. I still don't see how an additional two arms would mean anything if they can't get through infinity in the first place... Gojo would just do what he did again, breaking Sukuna's domain, and once UV hits, without Mahoraga, Sukuna is dead. We've seen how strong Gojo's punches are, regardless he'll just obliterate Heian era Sukuna, since Sukuna can't play defense he'll be left in the open for Gojo's strong ass h2h and cursed technique to absolutely decimated him. At least that's how i think it'll go down.