I've done jumps of 2-3 patch releases in VRF backup/restores, but not as far back as 7.6. That's a pretty big jump.
Assuming you've gotten a new server to do the new install, keep the old setup online for a bit & save off the backups externally. Then you can give it a shot on the new server before adding devices.
Alternatively - you might also try opening a TAC case and sending them a copy of your VRF backup to ask if they can try restoring on a lab setup with the latest release.