5'9" 265lbs bum Toney?
Boxers will usually always get grabbed and tackled. It would take a lot of brutality for a boxer to be successful and the rules of mma do not permit what it would take. The octagon rules favor the wrestlers.
I've got an Irish pal who fought Roy Jones Jr for the national amateure title (lost by decision), he thinks that in order for boxers to do well they would have to illuminate the gloves and just use hand wraps. That's not a good idea.
An elite boxer would just have to learn takedown/grappling defense.
See early-days Chuck Liddell.
He was knocking out grapplers left and right because he used his wrestling background to STAND BACK UP every time they even kinda got him down.
An elite-level athlete is elite-level because of natural talent and discipline, not because of choice of sport.
An elite boxer could become an elite grappler with the right trainers.
Of course, that river runs both ways, and the hardcore grapplers have to become at least mediocre strikers to have a chance, and many are going the extra mile and becoming awesome at it.
See this past weekend's fight between Fabricio Werdum and Travis Browne for a great example.
And with boxing gradually going the way of the dodo, more and more boxing trainers are turning to MMA gyms to earn their keep.
The best example of this IMO is the partnership of Matt Serra and Ray Longo in New York.
Also, Randy Couture making a sock monkey out of James Toney was a thing of beauty.