I'm not sure how much larger the flowmasters are than the mufflers (came as unknown make - model, but are large & loud) on my 69 FB, but as in the photo you can see there appears to be some extra room for an even larger ones, hope this helps. Most muffler shops don't list parts for 33 year old cars any more (not even the dealers, except some stock mufflers)so they're out on a limb when you come at them with these questions. You need to go to Pro's that specialize just with classic cars. Speedy cut a deal for my exhaust installed to the mufflers, 2 guys (over 40) worked almost 3 hours, all in for $200 USD - timing was right - came in on a slow day & they liked the car - timing is everthing!
