Always, Always, Always use the mounts for the CAR, not for the engine!!!
Your 64 GTO (assuming it had a Pontiac V-8 in it and was not subject to a chev engine swap) will have the correct frame mounts.
Your 70 455 block will have 5 motor mount holes per side. The two lower rear are for the 64-73+ A-body mounts (along with most other Pontiac models of that vintage).
The 3 forward holes are for the 70-81 Bird mounts which are different than all the rest (and some others in the late 70's, we'll discuss them below).
If your old rubber motor mounts from your GTO are in good shape, just re-use them. If you want new ones, they are available at any local parts store (ask for 64-72 Lemans V-8 mounts) for about $12 each. There is a left and a right mount (bolts that attach the frame mounts to the frame brackets go through from the FRONT).
Starting around 74, Pontiac re-designed the engine mounts so that the rubber part of the mount was in the frame bracket and the part of the mount on the engine was a solid steel piece of metal. Add in that Full size sometimes used a diff mount (and we already know the 70-81 Birds are diff) and you can see why you ALWAYS need to use the mounts for your car.
Last thing: Find another vender for parts or at least QUIT asking that particular one for advice since it's obvious they don't know Pontiacs.
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