Kramer,
I think you're set just as you described. That's what I have on the boat too but, i'm a halibut-catching rookie ha!

My only experience was with two 30-pound fish last week. Both fish I harpooned for the experience and tied off the 3/8 nylon line to the rear cleat. I had 20-some feet of line also.

With a bigger fish, I can't imagine that 17" bouy wouldn't be enough.
Once I slit the gill it was over pretty quick.

Good luck,
Jeff