#3 and Rozier for Okafor
Then #23, #52, and Johnson for Ibaka (Thunder have no picks and have marginalized Ibaka's role with the rise of Adams and Kanter, shouldn't take much.)
Running it back with the same team but with the 4 and 5 significantly upgraded.
I don't feel like you'd have to give up a talent like Rozier plus the pick to nab Okafor. If you do have to add something (it works straight across IMO) to #3, it would be one of your 2nd round picks.
Here's my proposal:
Philly gets: #3 & #16 plus (pick your salary filler)
Boston gets: Okafor plus rights to Dario Saric
I'd throw in a 2nd rounder as well, if needed.
Why Philly does this: Assuming Embiid is healthy, Okafor becomes tradable. Saric plays pretty much the same position and role (6' 10" scoring/point-forward) that Simmons would play. So both would be trades from surplus for them. Getting the two picks would give Philly the ability to take both Simmons and Dunn and still have three more first round picks (#16, #24 & #26) with which to round out and finally balance their roster.
Why Boston does this: Okafor would give us the long, skilled 7 footer we've been craving. Fantastic offensive potential. Not an elite defender, but physically has the potential to be one if coached into the right system. Saric would provide us an extremely skilled scoring point-forward with an incredible competitive nature.