Since jones travelled back to chapter 1 it means it was before his death in chapter 3. Chapter 5 is just another probably version of chapter 2 in the same timeframe.
I think Megalo Don is also Gunnar I think after the blast from Dr. Doom Gunnar was still alive but needed something to keep him going and since IO were gone he wanted to start an Apocalyptic crew so he did and then he still needed something to keep him going so he recruited an engineer named the Machinist and possibly wanted her to create Nitro and she did and then Gunnar upgraded his armor and put Nitro tubes on his armor and then changed his name to Megalo Don
The second I saw the trailer I got hyped, because Gunnar got thrown int the zero point, which IF YOU REMEMBER creates a snapshot of you, so in theory that him , or a snapshot