Don't know if it helps, but here is my 1997 250 with 2011 tank, the only modifications made was to move coil & grind out shock mount,top part.
Mikel sold me the Tank.
And also welded a plate to sit at the front of the frame, so the tank could be secured properly, I'm not sure if the 1999 300 is the same ? With the hole in the frame.