That wasn't quite plain sailing. Somehow I lost my ability to get into recovery mode. I still had download mode. Very odd. I was sitting on JM8 and unable to get to recovery. I've done this process before. The only variable was using the Odin3 v1.7. I had to think for a minute just how I was going to get to recovery since I couldn't root the phone using the ChainFire method.
I still had the full JPM version so I flashed that. Flashed CF Root, and was able to get into recovery mode. Next I applied the update.zip to get CWM. Then flashed Doc's JPX v6.1. I got FC errors on the start up wizard but it righted itself.
Now I'm restoring my apps with TB and I'm sure all will be right again. IMEI in tact, About Phone reporting I'm on the correct rom so just a bit of tweaking of homescreens etc and I'll be away laughing.