Upgraded the front and rear speakers with Vibe Slick6-V7 6.5 component fronts and coaxial rears.
I used the original speaker mounts modified to fit the new ones, you can use aftermarket spacers they need to be 34mm deep.
The tweeters need the crossover to work properly. The tweeters made a big difference to vocals, horns and percussion lifting the highs to a much better place. Just replacing these is a big improvement.
There have been reports that the rears only get a low pass feed but I haven't found that after some frequency testing, they are getting the full range.
The mid and bass is much better with good low end control and nice bass note definition.
I chose the Vibe speakers as they are easy for the stock head-unit to drive and will be ok for a future amp upgrade also. Vibe is a British car audio company that have Chinese partners for manufacturing so suit the MG :-)
The sound deadening is important and makes a big difference pulling the sound together cleanly. It doesn't need to be foil backed as I've used, I already had a roll of foil backed left over from insulating my sail boat (which I converted to electric drive!).
The wiring colours I suggest here are what my car has but should be the same so please double check with a volt metre for the + and - terminals to be sure.
The amp/head-unit is behind the glovebox and you can gain access to it by removing the glovebox, this is not needed for this upgrade, but may be useful if you want to add an amplifier so you can use the existing speaker wires.

Vibe Speakers
https://vibeaudio.co.uk/product/slick...
https://vibeaudio.co.uk/product/slick...
Pry Tools
https://www.ebay.co.uk/itm/155235712873