Add to your search list a '66 and '67 also as they are all very similar. In fact '65 and '66 carry the same part number. The '67 has different rear spring upper mounts, so you would have to use '67 tapered springs but other than that its a direct replacement. There is a slight difference between '64 and "65 but it only comes into play if you're using a big block.
Another option is a '64 thru'67 El Camino frame, which has a boxed center section the same as the convertible. The El Camino frame is identical from the front right back to the mount behind the rear axle then just a tad longer. Shortening it isn't that big a job.
Went thru this a few years back and went the Elky route.
Good luck with your search.
Ted