Here is a pic of the inside of my 65' with a 67-68 radiator support:
I use a 24" wide 67' copper small block radiator.
To be up front, this is not a bolt-in affair. It requires welding and you must do a little modifying. of the new support. It was not a tough job, but you need to have access to a welder and some tools PLUS you need to have the required skills.
I installed the 67- 68' radiator core in a couple of afternoons. The engine compartments are the same height so that is not a problem. The top matches the front aprons perfectly, as does the bottom where the cross brace fits. The sides panels near the fenders are much different. I needed to remove some material from the driver's side near the fender and add some to the passenger's side. I also needed to cut out the hood bumper "triangles" and graft them to the new support. Perhaps the standard 67-68 ones would have worked, but I did not have any and none were included with the new core support.
Other area of concerns consist of what to do with the battery once a 24" radiator is installed. I wanted to retain the battery in the engine compartment and so I made a battery tray by combining the top pan from a 67' and using the under bracket of the 65'. I could have installed the 67' fender apron which incorporates the battery in a different location, instead.
To use the larger radiator also requires using the appropriate mounts. I bought the 67' type mount for the top and made the bottom mount out of some C channel and rubber.
In the end it would have been much easier to cut out the old support and install a different radiator, but I am please with the results.
