In my experience....adding a properly-done step-bore (either 0.25mm or 0.5mm oversize) will add more HP to your 350F than any type of carbs you might add. As with all of these SOHC4 bikes, this engine normally picks up 10% more HP from a properly-done step-bore because of the warping of the cylinders, especially #1 and #4, which is normal in these engines. The #1 issue to watch during such a rebuild is: make DEAD SURE the piston-bore clearance is LESS than 0.001" (I use 0.0004" to 0.0006" max), as most machine shops will not do this tight tolerance unless you either insist on it, sign a waiver, or otherwise make them feel real uncomfortable. This means they must bore it so that the pistons will not fit into the holes until after it has been finish-honed, and the proper such finish honing removes about 0.0008", so this means they must bore to 0.0002" LESS than the piston skirt diameter prior to honing.
I rebuilt my own 750 with 0.0006" piston clearance, and it runs better than it EVER did.