It's been a while since anything was posted here in this thread, but a question was posted about using Buick V-6 motor mounts for a Pontiac V-8 swap in another thread
viewtopic.php?f=1&t=28983I am replying here, but each thread is now cross-referenced to the other.
There are 4 basic parts to mounting the V-8:
1. Frame Plates - these are large stamped steel plates that bolt to the frame rails.
2. Motor Mount 'Pads' - these bolt to the frame plates and have a 'longitudinal' hole in it with some rubber around it to isolate vibrations.
3. Motor Mounts - these bolt to the engine and have 2 'ears' with holes in them for the Motor Mount Bolt.
4. Motor Mount Bolts/Nuts - the main item is a long bolt that is installed through the 'ears' of the Motor Mount and through the 'longitudinal' hole in the Motor Mount 'Pad'.
The Buick V-6 and V-8 Motor Mount 'Pad' is narrower than the Pontiac V-8 Motor Mount 'Pad'. Also, where the 'Pad' bolts to the Frame Plates, the Buick 'Pad' has 3 bolts and the Pontiac 'Pad' has 4 bolts.
H-body.org member cammerJeff posted some good pics of the Buick V-6 Frame Plates with the attached Motor Mount 'Pads' here:
viewtopic.php?f=2&t=28788&start=6