For a drift boat, I'd go with the Yamaha 6/8 4 stroke. It's lighter and the shifter is on the tiller handle.
The Honda 8 is as heavy as their 9.9, about 100lbs.
I've got an 8HP 2 stroke merc for my DB (73lbs)and it works fine, but then again, it's a two stroke. I'd prefer a 4, but when I bought the boat, the seller wasn't willing to seperate them. The motor was brand new, so I figured what the heck.
The Merc 4 stroke is a much bulkier motor than the others, which probably isn't a good thing on a drifty. Othewise, it's a sweet little motor too, ask Hogmaster!