Normally I never touch Apples but my Dad asked me to sort his so I thought I would have a go.
It had Lion on it. I managed to used the Boot Camp Assistant to download the Win7 drivers and then install Win10. Things seemed reasonably OK, but sound drivers don't seem right as volume is very low, and Apple Software Update didn't install in Win10.
Then ask part of my messing around, I've removed the original HDD and fitted SSD, done fresh install of Lion, then installed update to Yosemite.
I was hoping this would get me a newer version of Boot Camp Assistant to get proper Win10 drivers, but no joy. I seem to have even gone backwards, as now Boot Camp Assistant doesn't like the USB stick formatted in FAT that it previously worked fine with.
Anyone got any ideas on how I can get the proper Win10x64 drivers for this (or how I can get newer Boot Camp Assistant to work)?
I've only ever done this once and on that occasion I replaced macOS with Windows. I can't recall any issues, and the steps Itook sound the same as you:
Downloaded Windows support software using Bootcamp Assistant to USB
Booted to Windows DVD (this mac would not boot from my iODD emulator so went old skool with a physical DVD)
Deleted any existing partitions and installed as usual
Once installed ran Apple software from earlier step
Rebooted - this corrected resolution
Part of my notes say this model only supports Windows 7-8.1, have you checked what yours can take using everymac? [Only registered and activated users can see links. ]
Turns out it was actually an early 2011 MBP so officially only supports High Sierra/Win 8.
Went through a gradual process of upgrading from one OS to another to another until laptop was properly set up with High Sierra. Luckily I cloned the original drive as at some point it seems it changed from GPT to MBR which stopped me from being able to upgrade at one stage, so then I had to put in a fresh drive and do a fresh install of Yosemite which I then managed to upgrade. I can't remember exactly when, but at some point, doing the upgrades stopped the automatic internet recovery from working - laptop would say it wanted to download Lion from internet but would always fail. Now after doing everything properly internet recovery will download High Sierra instead.
Then I found
[Only registered and activated users can see links. ]
which let me create a patched Catalina install USB stick, used that to do a fresh install then successfully set up Win 10 using Boot Camp.
Was a little disappointed as one of the main reasons I wanted to update the MacOS was to get proper Win10 drivers, but it appears the latest version of bootcamp that supports Win10 and the older version that only supported Win8 both use the same set of drivers. Also the stupid installer installs all the drivers, even the ones that weren't needed, so I did a dummy run installation of just Win10, found out which drivers I actually needed, then deleted the unneeded drivers from the USB stick, then installed Win10 using Boot Camp.
So project has been completed totally successfully in the end but I think I'm never messing with a Mac again, although just to be on the safe side in case I ever get made to do a Mac again, I've made some USB install sticks for Catalina, High Sierra, and patched Catalina.
Just the fact that some geniuses were laughed at does not imply that all who are laughed at are geniuses. They laughed at Columbus, they laughed at Fulton, they laughed at the Wright brothers. But they also laughed at Bozo the Clown.