If you got the motor and the money go for it, supercharge away, but if you got more money, buy more motor. If you were to put that same supercharger on a 350, you would be well on your way to your 400 horse range. Proving someone wrong isnt always the way to go, sure you can get that horse but your gonna have to realize you can only push that motor so much til your at your limit, in my opinion buy that supercharger since it can be used on more than that 305 but DONT buy heads for that 305. The chamber and valve size will hurt any bigger displacement motor if you ever decide to swap, good luck