I did a V-8 swap on my '64 but it had side mounts that I reused for the 350. I presume the frames would be the same from a '61 to '64 although the suspension is different. I would find a donor truck in the '63 to '66 era and pull the engine mount towers. Then go to a parts store and get engine mounts for a '66 equipped with a V-8. Put the engine in and mount it to the trans. Put the engine mounts and towers on the engine and lower it to the frame. Center the engine, drill the holes in the frame and bolt it down. I love my new found power. There's no replacement for displacement - good luck
