Why not play SMS games on a Genesis with a capable flash cart? The Game Gear exclusive roms have been modded to be enjoyed on a standard screen, and you can still get a power-base convertor to play nearly all on a Genesis with it's built-in RGB output.
I have original Game Gears that I refurbished, then I bought a flash cart that can play SMS games through them. It's not really great. After making the third work through recapping it's still a little unreliable. I have now bought 4 of them so I could play through a couple of exclusives. It was an experience for sure, but not recommended.
The McWill LCD upgrade is not capable of 1:1 or 1:2 scaling, it's a non-integer scaled pixel mess. Do not do it.

I know the original hardware is preferred, but the flashcarts can easily bypass the genesis hardware and make the SMS roms play with even the FM hardware being now faithfully reproduced.
Can't recommend original hardware here, It's failing and hard to refurbish.
You can consolize a Game Gear if you need to play the exclusives without dealing with the screen, but it is one of the most involved mods.
Having said all that, if you want to buy my Game gear(s) to play a couple of games, I'd sell all of what I've got at a loss - PM me. The LCD is as gloriously viewable at only one angle as I remember it being in the 90s, but it's still bright and colorful through the new glass screen. I think it needs about 11 degrees from original angle to get the full color when you adjust the potentiometer. I guarantee the sound hardware to be fully upgraded, and you will have all of the SMS games in a single cart.
Still underweling IMO, but you seem like you'd enjoy the original experience.