As it happens, whilst I had my computer apart, (also a G750JX) I replaced the DVD drive with a blu-ray drive (from a broken HP).
It plugged straight in. The only thing that differs is the brackets that are screwed to the drive, and they are easily swapped over.

BUT, here's the weird thing:
The drive in my G70 is fitted with a single retaining bracket. It is fixed to the inside (plug end) edge by two screws. A single "retaining screw" is then screwed into this bracket.
If you remove the cover over the HDD's & RAM, there are two holes near the RAM marked "B" and "C". On my laptop, the retaining screw lines up with hole C.
However whilst there was a screw in there, it doesn't actually attach to anything on the laptop.
SO, I can actually pull my DVD drive in and out without removing the screw!!!

I'd be interested to know if anyone else has the same setup.

But either way, swapping your DVD drive is easy, and any normal laptop drive should fit.

NB: You will also need to swap over the plastic facia.
(In my case I swapped it for a blu-ray SLOT drive, so the facia is different. Looks a big ugly, but I prefer not having the DVD tray pop out every time I bump the button.)