Some rookie questions

I'd start with the items that will need to be changed if you DO increase the power. Disc brakes, better rear axle with a performance gear ratio, electronic ignition, and maybe a suspension upgrade if this is going to be a street car. Do some research on slant 6 upgrades for cost vs improved performance to see which one fits your budget. Keep in mind that some "upgrades" will effect driveability, mileage, and reliability.