The 65 Wildcat and 65 LeSabre had different wheelbases, all differences were forward of the firewall! you may have some trouble with the length of the nailhead vs a 300. The 64 Lesabre wagons were completely different animals...built on 64 Wildcat chassis which were x frame.
Since the nailhead did fit into the Skylark 300 frame, my guess is that to meet the same engine mounting points with the nail you would have to use the same kind of mounts as the Skylark GS...i'm thinking those mounts effectively moved the mount position back from where they are on a WIldcat 3", which is the same amount the frame is different from the LeSabre! :clonk:
EASIER TO get a Wildcat and put Lesabre trim on it :jeez: