I haven't done it, but straight through exhaust has been done plenty of times. General consensus, from what I've gleaned, is that 2.5" or 3" mandrel bent exhaust without mufflers is the way to go. Personally, on an otherwise stock motor, I doubt you'll see gains from going 3" over 2.5". This motor just isn't that big. It won't hurt to go bigger, though you'll have an easier time packaging the 2.5" stuff. The biggest contributor will be the mandrel bends versus stock crush bent tubing. Check out the builder kits over at
Tube Bending & Fabrication - Columbia River Mandrel Bending.
Not to say that you won't feel a difference, but stock exhaust isn't
that bad, anyway. Bang for buck, you'd be better off getting a manual boost controller (ebay it), bump it up to 14psi, ALDA adjust/delete, rack limiter adjust/delete. From anecdotal evidence between different owner's observations, it's good for +20-30 crank hp.