My brothers were quite a bit taller then the cab. 2 feet maybe. Gave him crap about them being too tall. After he cut them down to about a 10" taller then the cab it got real loud in the cab. Before it was no different then 4" straight under the truck. Caps are easy to find. I would call I80 to, they are just up the road a piece from here.
I'm gonna put stacks on my 90 after I get a flat bed. Going with 6" miter cut flush with the cab. But mine will be for fourwheeling, can't have tree limbs modifiying the exhaust. Mine won't be a daily driver either. A little (lot) of noise is ok for my toys.
Michael