You can still do a system repair from the installation disc in Win 7, it's just a slightly different process... it begins in Control Panel rather than going to Settings as per Win 10. Also, have you tried scc /scannow to detect and repair corrupt or missing system files?
I've not been able to test this because I no longer have a copy of Win 7, but it might be worth giving it a try. I recall reading somewhere that Win 7 recognises M.2 drives if they're mounted on a PCIE expansion card because the hardware signature is different to the on-board mobo M.2 slots. If it works then you should be able to remount it in anon-board slot.
Nothing's ever that easy....when you cannot see the booted system due to GPU failure and bad driver you can't do sfc to fix safe mode...and you can't get to safe mode.
7 doesn't recognise a M.2 card direct to MoBo as in a X99 so the install disc doesn't work either.
What I did...but haven't checked yet...was to boot into the original SSD OS  and access a second [imaged drive] of the M.2 ...also on a SSD and copy/pasted the driver files as an experiment to see if I could 'externally' correct safe mode on the image. If that works I can repeat it on the main OS M.2.
However....$1111 AUD later and I replaced the GPU and after the usually hissy-fits have convinced the M.2 OS to behave....and run. It still has a dud safe-mode...but I may yet solve it.
The next step AFTER I win against MS is to use the image OS drive to upgrade to 10 ....and see how much of the system is FUBARed by that.
If I survive I'll repeat it on the M.2 .... and needless to say, 10 won't have an issue with where the M.2 is plugged in....as the OS is newer than the drive format.
It's good that this is a 'hobby'....
Latest entertaining bit....the RTX3070 is not an issue with length....not an issue with height...but the 2 8pin plugs are an issue with width....on the Level 10 case.... so I have some case modding to do....not drastic...but reversible...