I believe this was one of the factory options, but that cabinet becomes really heavy this way.
It sure do!
During the '80s my main amp for rock/pop gigs was a Fender SS Showman, claimed 200 watts of big-iron class A/B, factory equipped with an EV-15L, weighed 72 lbs. After playing it for a decade I decided to replace it with a Mesa Boogie MKIV. Daddy's Junky Music had just gotten one with an EV12L, just the way I wanted it. After driving them crazy for a few hours trying it out I was ready to buy it until I tried to carry it up front. I thought it was nailed to the floor. It was hard to believe that little thing weighed as much as the Showman.
I had a brainstorm--buy a head and cab, more total weight in lighter pieces. DJM refused to order me one so I placed the order with my usual guy at Chuck Levin's, Mesa dropped shipped it. I had liked the Fender, but the Boogie just beat it in every weigh (OY!)