Originally Posted by jaw22w
You mention 20" as the width of the frame. This is actually too narrow for a 350. My frame measures 23.25" at the front of the engine and tapers to 27.5" at the cowl (inside dimensions). The mechanical fuel pump is only 1" from the frame rail and the low mounted alternator is about 1/2" from the frame rail. This is on a 27T, so the car is narrower than what you have, but you still need the space for your engine.
20" is too narrow if you're going inside the rails with headers, or using a mechanical fuel pump, and keeping the engine low in the rails. But my frame is that narrrow and I'm using fenderwell headers and an electric fuel pump, and it fits great.