Well I've never owned a truck new enough to have to "delete" anything BUT My thought on your situation is whatever you take out should be replaced with a muffling device of comparable effectiveness for the most stock,like sound... replacing the entire exhaust won't help your cause as all...
EDIT:
I googled it and it looks like superduty seats in an OBS is no problem BUT I do see an issue.....
If you look at the pic (HERE) of the back seat installed, the floor humps up alot under it.... with the 60/40 rear seat there is another bracket and hinge point between the 60 and 40...