Sorry it took so long to post the solution to this. Jon I think actually posted it.
K,
1) Using the track selection tool select all the multi cam clips in your time line that you want to convert to HD
2) Right click and select replace with AFter Effects Compostion. After Effects will open up with the the comp loaded up.
3) Open the Multi Cam Composition and adjust settings to hd. Do the same with the Nested Comp.
4) Export the project as a Premiere project under file export
5) Open the project in Premiere. You’ll need to remember which cuts use which camera because exporting from after effects reverts all the multi cam clips to camera 1