One sure change is drivers floor pan. Don dropped the floor and made it out of metal vs CR I fiberglass. The CR I used Mustang II style motor mounts which nobody would go back to but a CR I might have upgraded to CR II mounts. Don added angle behind seats not sure when but it’s in the threads. Some of us CR I added it but lack of angle would indicate CR I. More changes Don made are in the threads
Was curious, so did some late night digging around the internet. Found some interesting info/pics: http://www.classicroadsters.com/index.html
and : http://sebring-mx.com/
You can click o the C427 etc., some interesting photos, prices etc., not too much on second site. all part of the convoluted history.