The 300 won't fit on a 250 swingarm without some serious mods.Isn't it the same frame as the late model Mastiff's? if yes and the rear fender tolerates it, you can look at 300 on the back. The rear fender from a Mastiff or K9 would work as well if your fender is curved wrong for the 300. There was a Mastiff or K9 rear fender with struts on eBay just a week or two ago. (maybe that was a sissy bar with struts).
Just an idea to kick around.
I think the mastiff front is a 3.5 may not fit in your fender. pits,choppers and 04 ridgeback had 2.5 fronts you'll just have to watch the year on the pitt and the ridge cause they both went to 300 rears.PM me with a price . How wide is the Mastiff Front ? Send pictures if you can