Simmons for Markkanen and Dunn makes them a much tougher team to guard. In a vacuum, Simmons is a better player, but Markkanen would be exactly what they would need.
I just think a 5 of :
Markkanen - Butler - Embiid - Dunn - Redick
Looks a lot better in terms of fit than :
Chandler - Butler - Embiid - Simmons - Redick
I think that's a fair offer, but if I were GM of the 76ers I would demand a bit more. Just because you can! Simmons is still perceived as a franchise type player. Maybe expand your proposal:
To Philadelphia: Markkanen, Dunn, Portis, Lopez + prot. 1st
To Chicago: Simmons, Chandler, Korkmaz, Johnson
And then I would ship Fultz for a solid 3 and D guy (X).
New rotation: Dunn/McConnell - Redick/Shamet - Butler/X - Markkanen/Portis - Embiid/Lopez
Of course if I were really the GM of the 76ers I would run them quickly to the ground and pick up my ransom when I'm fired