Normally, Sanshou fighters would have a focus on speed and technique, not strength. But this guy being a(n ex) powerlifter, I can probably imagine he brought that mentallity with him into martial arts. He's probably still trying to jack on some more muscle now as we speak. I would guess that that weight advantage of his is pretty much all muscle. That really means you'll have to use your cardio to your advantage to burn him out. Make it difficult for him to use that strength advantage of his.
So I'd say make that Friday another cardio-oriented day, is what I'd say.
If he's pure Sanshou and not a thing else, you could go to the ground. I don't know how confident you are in your ground skills, or in your standup, or what you favor. But I'd say the best bet is to stay standing with him for the first round and dance around with him to burn him out. Once he's slowing down, take it to the ground where he's just going to get more and more tired, and where you'll probably have the skill-edge. Sanshou has no ground work to speak of.
Use your own judgement though, and be prepared for whatever may come.
I don't think four months is too far out. Just don't let yourself get burnt out or overtrain to injury.