Hi Tim. I just saw this posting today or I would have shared this knowledge sooner with you. I did this exact conversion about 32 years ago on a 1968 Coronet 500 Convertible that I was transforming into a Coronet R/T. I wanted an R/T Convertible, A 'Modified Replica' as they didn't even call them 'Clones' back then. I had a 1968 Coronet R/T that was very rusted out to use as a donor car for the project. (I know I know, but this was 32 years ago and they weren't so sought after and expensive as they are now ) The ONLY thing I had to adapt were the two small upper tabs located on the Rally Dash frame. I measured precisely where they were both located on the R/T frame. I then cut them out and used a small oxygen/propane welding kit and welded them onto the upper portion of the 500 Dash Frame. From what I remember this was all that was necessary. It's not an original setup because Convertibles didn't have a Rally Dash option but back then I didn't know that. No computers back then. Anyway, nobody will be parting with these tabs on an original frame so you'll have to make them yourself. See if someone here can get you the measurements of the two upper tabs on a Rally Dash frame, maybe some photos too. And the thickness as well. You'll need to get a little sheet steel and cut them out to an approximate size and shape as the originals are. Then compare what you have with your frame to see where they would attach to. This is done with the gauges and speedo removed of course. If you have the precise place where to weld both upper tabs on your frame, once you've made these two pieces out of a thin steel ( nibbler or grinder ?) and welded them in place then just drill a small hole in them where the screws will attach. Test fit the Rally Pack first to see and mark where to drill. It's not that hard depending on your abilities. Good Luck to you.
