That's what the early UFC fights were. There were no weight classes back then. Names were drawn for the tournament and you fought who you fought. Keith Hackney fought Emmanuel Yarborough at UFC 3, Sept 9, 1994. Hackney is 5'11" and weighed 200lbs. Yarborough is 6'8" and weighed 600lbs. Hackney KO'd him in the first round.
It would never happen today. No state athletic commissions would sanction it. Back then it was style vs style. Today the fighters are well rounded and much more dangerous. A 70 to 100lb+ weight difference between fighters could have catastrophic consequences.