Here is an Ebay auction for a used C5OE Hipo harmonic balancer by Ebay member "mustangmasters428" with a starting bid of $395.00:
Here we have a 1965 66 or 67 hard to find factory original C5OE 289 High Performance Harmonic Balancer. The Ford engineers felt it necessary to add the extra balancing to their 271 horsepower 289 Hipo 4 barrel power house. These hard charging motors received heavy duty rods and special crankshaft which demanded a thicker, heavy duty balancer for this high revving motor.
A signature item of all 289 HiPo's, Ford also carried this design into their 68 J code 302 4v's which were used in GT 350 Shelby's changing nothing but the part number and adding proper timing marks. This item is also correct for a 68 GT 350 Shelby, and would make a good spare if not replacing your original unit.
This part is an original C5OZ not the later C8ZE-6316-A offered by Ford as a service replacement part after they depleted their stock of original C5OZ's. Coming to you in good used condition free of gouges or stripped threads and rubber in good shape, we feel this unit will make a great addition or replacement for your worn or tattered original, and will bolt right on with no modifications and perform as originally designed. Whether as a spare, or as a replacement to get your car on the road, don't let this one get away as these are getting hard to find!
https://www.ebay.com/itm/65-66-67-C…V1bg2Cw&vxp=mtr
-Fred-