1966, yes the originals are pricey. the 1st set I bought for the 350 in my '66 was oem and I paid $225 if I remember right. after one broke (my fault) I replaced it with a $59 aftermarket. I'd say, if you don't need brackets buy the set without them.
how does the HeartThrob system attach at the manifold end? since the ramshorns take a pipe with a end that's built for a donut gasket with a stub pipe that fits up into the manifold, you'd want to make sure the one's you buy are the size you need. Zoom in on the ones in your link
http://www.ebay.com/itm/201120760217. notice the machined area where the exhaust pipe fits.
those in your first post look like 2" to me but jtrichard may be right.