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the Dynomax kit should clear the crossmember no problem. its made to fit the truck(at least it should fit)you will probably need 3" to 2 1/4" header reducers. i doubt they come in the kit. you may also need to make/buy other little things. like hangers, clamps, ect.and i dont know if they are all like my truck but when i put my headers on i had to use a spacer and reuse the stock manifold bolt that is used to mount the power steering pump
Pipe sizes are good. There are people who will tell you to go at least 2.5", but that's not required. A normally aspirated 5000 rpm 350 just doesn't pump enough air to need more than 2.25".