67 & 68 396 frame mounts move the motor about 1 " forward. That's why they have a longer driveshaft. You said you have a 67 l78 already so the frame mounts should be correct. the correct bb frame mounts just hang over the back edge of the frame while sb's hang over an inch or so. Just buy 67 302, 350 or 396 motor mounts and the motor will set correctly. Sounds like you also have a small block crossmember. If the crossmember has an oval opening where the bolts are then its a small block one.
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