67 through 73? (What ever year was the last to use the biscuit) SB do sit close to the block.
66 and older are different as the k frame is different.
There is also a possibility that you have a /6 k frame in your 66 and the mounts are swap mounts.
As stated above swap the metal mounts and rubber isolators (biscuits) that were in your 66 now on to the new motor.
Assuming the old motor in the 66 fit correctly.
BTW...
I don't know if this will effect you but it was pointed out that later smog motors have a extra pad under each exhaust port for air injection and 66 and older stock exhaust manifolds hit it preventing the manifold from seating.
1965 MOPAR, 273 Exhaust Maifolds.
