Same situation here. I ordered our '99 with the HD case but diesel option locked out the plow prep option. So we did it the Johnny Cash way - - - one piece at a time.
So the truck comes in with the "built especially for XYZ Snowplowing Company" on the sticker, with a follow on comment: "Note: This vehicle not equipped for snowplowing. "
He, he, he - - so far, so good. We did lose the torque converter this summer, but no other major problems. We did have the heavier springs installed as well. Two seasons of plowing, and the truck works like a dream. The only thing better would be a loader with an 18' Daniels blade.