Does anyone out there know if the VIN # was also on the engine for a 1965 Buick Riviera (425 engine). We're trying to find a way to ID ours.

Yes, the VIN is stapmed on the front top of the block. Click on the 'shop' section above, go to 'Identify Your Buick Engine',and see the section on 'where to find the numbers'. The picture there for 425's is for a 66 model, but yours will be very similar if it has the original 65 engine.