I was about to point you at the Avon Leisure website, but it looks like thay have either reduced their range somewhat, or half of it has dissappeared into the electronic ether...
In the absense of any printed data, measure vertically from the transom top (or well if it has a cut-out) to the bottom of the "V". If the hull is rated for 30Hp It will either be in the 20 or 25 inch ballpark.
As for the cables, the Teleflex website has (had?) a good PDF explaining how to measure up for a new cable in the absense of an old one to pull out. Actual length will depend on routing, console...
