i now buy a new route r2116 and cant put it new version, its just a hard work to do it. I will try to manually upgrade it to v7 like you propose.
If I had to migrate from CCR1036 v6.48.6 to CCR2112 v7.7 (I would not choose other versions)
1) I would take another CCR1036 which I already would have as a spare.
2) I would configure it with v6.48.6 identical to the one I have to replace (so I would also have an immediate backup)
3) I would upgrade from 6.48.6 to 7.7
4) I would export the configuration with show sensitive (no backup)
5) I would netinstall CCR2112 with 7.7
6) using the export generated by CCR1036 updated to 7.7 I would configure CCR2112 section by section.
7) I would test the device by placing it in an unimportant part in production, with a backup rig already ready.
After a month of testing, I would replace the CCR1036.