Your best bet for upgrades would be through Taigen Tanks
https://www.taigentanks.com/ Erik works there and is a good guy and is active on the forum.
Check out their website, they are out of Florida. Their newer gearboxes are good upgrades.
I can't help you much with the guns, as my Tanks are IR. You should get plenty of help here on the forum though.
Just ask away and be patient, many of us still have full time jobs, lol. Maybe start a thread on a specific question
otherwise the responses will be all over the place.