Joe, it's definitely ok to flatten them before drying (and this will help them to dry faster); just know that you'll need to do it again after they are dry (due to wood movement during the drying process). If you install a butterfly now, it might become loose as the slabs dry and shrink. Better to take some strapping and nail it across the ends of the slabs to prevent the checks from splitting further.
Okay, now I understand Joe's rationale for flattening the slabs before the drying process. We all continue to learn from one another and that's a good thing. ccasion1 My thinking was to sticker and slowly air dry the slabs even with the chainsaw "bumps". They'll have to be flattened later at the end of the day in any event.
Thanks for all the replies everyone. I have thought about cutting them in half but at least one of them I want to leave really thick for an end table Roy.
William I've been using my small 18" chain saw to cut them into boards but that's all done with now that it's maneable. If I were to re-saw in half I'd go to my buddies shop and use his ginormous band saw.
Scott thanks for the insight on strapping the ends to prevent further checkering and splitting. I'll definitely do that. Do I just use compression straps like the ones you use to strap things to your car?
--Joe