outboard shaft length for a willie DB??

have a willie 16x54 drifter and am getting a 8hp what size shaft should the motor be??

Dampainnter, When I picked up my Willie two plus years ago I asked the same question, and without hesitation the salesman said"long shaft". So, after two years of running it on the Quilayute in the second tilt hole up position I have not hit bottom yet with the prop. I'd just call that luck and a lot of knowledge on Willies part. Hope this helps, Sid.