The best you can buy and only poly urethane pre mades for the 66 are these
Unfortunately they arre around 200 bucks.
What I did is replace them with OEM style rubbers becasue they are 20 bucks from most parts houses and built a toque stratp from a turnbuckle on the drivers side to control the twisting and not overly strain the rubber mount. Like this.
The turnbuckle cost me less then 10 bucks and then i had enough steel laying around to make the brackets.
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PS DON'T jack it up by the balancer if you are going to test it with a jack jack it up from the bellousing.