Was playing around with the idea of running Guass on the Bushie, started off with the X2 with a larger engine and only the 2 lasers, ended up with the P2 and a lighter engine. With ammo cap it's just enough, you could strip a little more armour off the legs to load another half ton but that's always risky on a Bushie.
I think I'd go and put the ammo in the torsos. Gauss ammo doesn't explode, and it pads the weapons, which do.
The ammo looks a tad light. May be with the increased values it is ok. You could reduce the engine to sneak a bit more in if you find yourself running out. Also, XL 255 weighs the same as the XL 250.