Those early UFC tournements were carefully planned by the Gracies to ensure Royce was up against people where his BJJ would be at a huge advantage. But an elite, World class athlete with the speed, power and timing of Tyson is on another planet to the likes of Art Jimmerson, Ken Shamrock and Dan Severn, even if he only knows how to strike. I would imagine Tyson to be too quick and therefore get his shots of before Gracie can initiate anything.
Kimo had little to no training before he fought Royce. Royce won, but a struggle against what was just an overall good athlete. Nothing really when compared to Tyson.
Hard to think Tyson was serious. Maybe he was. However, believe Gracie would have been knocked out easily in a match with Tyson.
Was Tyson also being humble when he said there's no way he'd be able to defeat Ali? James Tillis gave him some trouble and he's similar stylistically to Ali (though nowhere near Ali's level). Tyson did get better at fighting against the more classic boxer style later on. I don't think Tyson would beat Gracie UNLESS he was trained in knowing what to look out for. Gracie on the other hand won't be stupid enough to engage in trading with Tyson. If they tie up and clinch I would give the Gracie a huge advantage. If it doesn't go to the clinch then Gracie is gonna wake up with blurry vision and lights shining on his face.
Tyson would need 2 years of mma training , and a lot of grappling defense. Maybe even in 6 months he could of possibly ko royce on the ground; but truth be told, even if Royce would have beaten tyson, tyson is still a better athlete and had more potential as a mma fighter than Royce could ever had reached.