Axle swap on a '99 3023

I found that for about 500.00 I can get an axle that will handle up to 5k lbs. and
is the same as the one the factory installs on the newer 3023's with the 15" wheels. Has anyone done an axle swap? Trailmanor Engineering told me I will probably have to cut away the floor to make it work. I didn't think that going to a 15" wheel would need that much more width. The axles are all custom made to
order, they do not stock any axles at Dexter.(according to the website) Any thoughts??