if using the Sportsmans, get the 64cc & use a forged flat top piston that will give you about 9.5:1 with that head.
If your looking for 350 HP. your gonna have to have a pretty healthy cam, something that will run in the 6200-6500 range, unless you go with a hyd. roller , but that may be out of you budget.
Dont forget, an engine like this is also going to need a loose convertor & is really going to want a gear a little steeper than what you might have. John