I have always heard/read that nosecones do almost nothing until 70mph. They do however look cool. As with any setback of the prop it really does not do much unless you raise the X-Dim. There was a company that made a jackable extension box back in the early 90's. It moved it up 1 or 2". This probably went the way of the Do-do when Imco shortys came out. Just like adding a jackplate to an outboard but keeping the height level...can't see it doing much.
Shoot...This A-hole revised an 8 year old thread and here I am commenting on parts nolonger made.
Nick
1994 22' Classic-454 B1 Red & white
1981 13' Whaler sport(original owner)
South Tampa Bay, FL "May I mamoo dogface to the banana patch?"