Here is an Ebay auction for a used pair of Hipo exhaust manifolds by Ebay member "gt289gt390gt500" with a Buy-It-Now of $900.00:
Orig 1965 1966 Ford 289 Exhaust Manifold HIPO High Performance K Code Mustang.
Good used pair of original HIPO Exhaust manifolds
Original assembly line parts
Plus other factory casting numbers
Date codes are faint. looks like 3-27-5 and 3-15-5.. please look at the pictures, deciphering required. Dates are not clear. Looks like.... Please look at the pictures.
Original dirty finish....
Not cracked or broken.
Two exhaust studs replaced.
Original parts ready for your restoration.
Shipped FedEx, insured and signature delivery required.
Lots of packing