I'm going to use Oval pipe on mine next time I build an exhaust system for the '64 Riv. Otherwise I'm not sure I get a 3-3.5" pipe over the axle between tires and springs. As far as the Flowmaster kit, its designed for the 58-64 Chevys so its pretty much just a parts source not a bolt in. That is why I went for the TA kit because its pretty close to fitting.
I think the single bend that TA uses over the rear axle actually clears everything better than what I took off, which had two smaller bends. The right front pipe was way off though. Seems some of us received front pipes that worked fine, while others like me received rear pipes that don't hit the tires. So one could technically piece together a system that fits with no mods.
Anyone used Waldron's exhaust systems? They're about the only ones to repop the '64 Wildcat dual exhaust muffler.
I still have the stock 2.25" pipes on mine, but replaced the collectors with new SS and brand new Magnaflows. They're a few inches shorter than the stock mufflers, but they fit fine and sound tuff. Here's a clip I made of mine at idle:
