If the aftermarket that has built up for V8 conversions for the Jeep Wrangler is any indication, the MOPAR V8 fits inside the SUV. Jeep has confirmed that the Hellcat V8 will fit into the Gladiator, which essentially has the front of a Wrangler. The catch is that shoehorning in that Hellcat engine leaves no room
Jeep North American head Tim Kuniskis says the Hellcat V8 fits like a glove, but that is the issue. There is no space for energy absorption in a crash. I think many Gladiator and Wrangler fans would be just as happy with a standard Hemi V8.
The man also says that Jeep is guaging interest in a 2-door Gladiator of the J6 concept ilk, but that the ride is unlikely. Few buy 2-door trucks these days, but the same could be said for SUVs, and many own the 2-door Wrangler.