Then it looks like someone used the wrong BIOS image for your replacement MB. I have not seen a JH BIOS working on a JW MB before but I already knew it was possible due to the fact both notebooks don't support Optimus. So it's easier for a different GPU to be used with an unsupported notebook configuration of the same series of model. It just comes down to the drivers not installing.

Anyway,

You have 3 options available at this time.

Now I haven't attempted doing a recovery exactly like this one, so I can't say if forcing the JW BIOS to flash with a data mismatch error (because there will be one since there are 2 different BIOS images) that you'll POST after the flash, even though you'd be flashing the correct one instead. Using SW to do that would likely result in a brick due to a verification signature check failing at the end (possibly). This means a HW programmer would be the way to correct it without taking that risk of potentially having down time with the notebook should you be unable to boot afterwards. If it does work, then it means you can install your GPU drivers without having to modify them.

The other method you can try is with the BIOS recovery tool, specifically Easy Flash Utility and the key combo with the correct BIOS placed on a USB flash drive (formatted as FAT32) procedure. This process requires the notebook be turned off first, proper BIOS image copied to the root of the USB flash drive with it plugged in. Then HOLD the CTRL+HOME keys down together, then press the power button and remain holding just the CTRL+HOME keys down until you are greeted by the Easy Flash Utility screen. At this point, let go. It should begin flashing and power cycle on its own after it's complete. This may work or it could shutdown during the flashing process and still have to be recovered with a HW programmer. This is safer to do than the first option because the BIOS recovery procedure is set to force flash without security measures like specific register range write protections being enabled.

The other option which isn't risky at all, is modifying your NVIDIA drivers INF to work with the unsupported MB BIOS and GPU combo, specifically the nvami.inf file located in your "C:\NVIDIA\DisplayDriver\xxx.xx\Win10_64\International\Display.Driver" folder. After modification you can then install the NVIDIA drivers for your 765M GPU successfully. I have created a guide about how to do this here if you wish to try it out.

Basically what the problem is that the NVIDIA display drivers are listed according to vendors/devices(HW IDs)OSes and driver packages. When a notebook model is released for example, by various vendors (we'll use ASUS in this case), NVIDIA will also release a supported driver (with updated IDs) so the installer can DETECT and install the appropriate driver and packages for that HW. Being as your MB BIOS is of a G750JH BIOS which had the 780M GPU, that GPU Device ID can't be found. Instead it detects the 765M Device ID which is paired with a different HW ID for that MB BIOS. So the only way around this is to modify your drivers so they detect the GPU for what it's being listed as according to the Subsystem IDs, which usually is just the Device ID of the currently installed GPU as per your screenshot.