Here is an Ebay auction for a pair of used Hipo exhaust manifolds by Ebay member "gt35067" with a Buy-It-Now of $1,200.00 or make offer:
This is a pair of original 289 HIPO exhaust manifolds.
I listed them as used because I am not 100% sure they are NOS so look at the pictures closely and decide for yourself.
They do look like they were painted once at some point.
I can see where there was a gasket mounted up against the exhaust ports and I can see where there was some bolts installed so they have clearly been on a motor, but it doesn't look like they have ever had exhaust flowing through them.
The bare metal areas still look virgin with only a little surface rust starting (see pictures).
I put my finger in a few of the exhaust ports and I got no carbon on my finger tip.
Exterior wise they look beautiful with no pitting to speak of. Only light surface rust hear and there.
The date code on the backside of the passengers side looks to be 5-15-5 (May-15th-1965).
The date code on the drivers side is not completely clear, but I can make out 27-5 (month unknown-27th-1965).
Overall a super nice pair of exhaust manifolds.
Box size 21x14x14 with a weight of 32 lbs.