Thanks everyone who commented on the previous post, I wanted to keep the screen stock as much as the new IPS is likely the objectively best choice; in case you hadn't seen, the polarizer was completely burnt and made using the internal screen a no-go.

I bought some cheap polarising film sheets and a bottle of isopropanol. Honestly the process sucks, the screen is fixed to the main motherboard so it's awkwardly attached the whole time that you're carefully trying to take the shielding off the screen assembly, from the you can pop it out and get to work. I kept dabbing some IPA between the polarizer and digitizer(?) and using a razor to get the damaged polarizer off. From there it's a long process of trying to make the polarizer as adhesive-free as possible; mine was pretty bad and I had to do this for the front and back polarizer. You can cut a new piece of film to size and get that attached to the back of the screen, reassemble and power the console on with a game. Then you can test which orientation you want the polarizer to be for a correct image, if you're doing this take more time and care than I did, mine now seems to have a slightly red hue but I can live with that.

Absolutely worth it to me, I love the Mega Drive and having one that I can use on the go (when I can figure a battery solution out) is an absolute treat!