Duster 3" Tailpipes

alright...here is the question. I have my 73' duster, with a 451 stroker , 3" exhaust with X-Pipe, flowmaster 40 series and dumps before the rear axle. I love the sound when cruising or gettin' on the pedal, but when cruisin' on the highway or in traffic below 2 grand, my ears pretty much bleed from the resonance. Has anyone put 3" tailpiles on their duster ( i was under the impression 2-1/4" was the largest size that would fit.) If so....can you show a pic. Thanks guys!