Re: WTB - pre 2000 monster seat.
There are 2 differences between the pre 2000 and post 2000 seats.
They are
1) The cut out by the tanks on the later models is a little higher (just slightly, it's not that much)
2) The post that goes into the back and is held in place by the lock is different. But one could swap the earlier/later posts as they are mounted to the seat pan the same way.
Now, after looking at that Hawk closely it's pretty clear that the person who did that mod actually cut down the front of the seat where it goes into the tank. From the images I'd say about an inch.
You will have an easier time finding newer (2000+) seats than older and I think since you're going to be cutting the top and front a little you will probably not notice the difference between the 2 earlier/later.
Please post pictures of your during/finished project.
Best of luck.