Was the factory exhaust the HiPo version with the Large 2.5 in headpipe, straight through muffler, larger 2.25 over-the-axle pipe and straight through resonator. Anything else won’t sound the same.
When I bought my 66 someone had replaced the HP exhaust with the 2 barrel pipes. Yes, it did sound like a pick up. LMAO 2" intermediate pipe and 1 7/8" tail pipe. THat's about Slant 6 size.