A 6 will always sound like a 6cyl no matter what you do to it. You'll have to learn to appreciate that unique growl.
There were no Super 6's(2bbl instead of 1bbl) in 68. I don't think these came to light untill the 80's. 230hp would be very optimistic of a stock 225. A 1968 318 was rated at 230hp.
BTW, welcome to the board.