Some years back I bought a pair of mufflers that were listed as NOS for 65-66 GT from NPD. However when I received them,they were nothing to what I was expecting.These mufflers are 4 inches in diameter,x 17 inches long, with inlet & outlet in line.The part number embossed on them is C4RA-5230-A,with FOMOCO logo.I have read up on just about everything related to 65-66 muzzies.I even have the Ford Master Parts Catalouge,yeah the real big ones that I use for book ends,but there's no reference to that part number.Can I use these for concours?Pete.