i guess you could try it like mikes, 9" should be enough, however when i first did mine, i used a 12" travel shaft had about 3 1/2" of splines showing sitting level, if i would get on a steep ledge and get on it that damn thing would always slip out. (thats why i say measure) so i ended up making a square one to get me by, since then i broke both yoke/flange ends off the square one at the same time, so i just bought one with a little more slip so i didnt have to listen to the damn square one clank when the front was locked in. now i dont worry about it.