i'd pick vonleh... he looks like more of a center than a PF, he's big and strong, and his wingspan is only 2 inches less than embiid, and his athleticism is similar. he's a truly elite rebounder and a hard worker, apparently he makes a lot of hustle plays. he does lack offensive polish, but, watching his moves, he looks like he has real upside, he just needs to improve his muscle memory in the post in real game situations a little bit, he has the grace and athleticism to make the moves, he just hasn't figured out how to do it consistently yet without traveling. he's fairly quick-footed - with proper training he could be an effective post player. also, his jump shot is solid, he has great form, he even shot well from 3 (with limited attempts).
i think he'd pair well with olynyk and sullinger, olynyk could stretch the floor while vonleh cleans up underneath.