The Jets are already using the same offensive system he used when he coached the San Diego Chargers. His son Brian is the Jets offensive coordinator.
And Marty also used the 3-4 defense during his time in San Diego, and that is what the Jets currently play. The Jets have been building a 3-4 defense the last three years, so it wouldn't make a lot of sense to move to the 4-3 now.
So Marty would essentially use the same offense and defense as the Jets, and this would really help the players because they wouldn't have to learn new playbooks.
Also, Marty had a lot of success with a quarterback nearing 40 in Kansas City when he had Joe Montana, so he would be able to work effectively perhaps with Brett Favre, if he returns.
But the most important characteristic that Marty brings to the Jets is great leadership and motivational skills, something the Jets are in dire need of right now.