I've seen Khamzat more recently listed at 76 and Rumble 77. Looks like you likely got your info from wikipedia. Either way they are very close.
"Tapology shows that Anthony Johnson owns a one-inch reach advantage (77 inches to 76 inches) over Vadim Nemkov heading into this championship fight in the semifinal of the Grand Prix."
"What is Khamzat Chimaev’s reach?
Khamzat Chimaev’s reach is 76″ and leg reach is 40″.
One thing with Khamzat's wrestling career is he had his best results at 203 pounds, kind of like Rumble's best results were at light heavyweight. Unlike Rumble, Khamzat is mad dedicated and that is why I dont think he will struggle hitting weight, even if at a class to low - Rumble definitely fought too low, but he struggled w/ structure, dedication, partied, drank, lived a 'haram' life style. No, he is not some 7 foot guy, but his dimensions are that of many light heavy weights and heavy weights - as tall/taller/longer than hw's like Bader/DC/Fedor/Cain.
IMO, it's not his size that is the problem or makes him rare - it helps, sure - it is that the guy can fight his ass off, is fast af, tough, cardio, KO power, is an Olympic caliber wrestler (tech falled an Olympian with ease) and is as close to the perfect fighter as you will find. I'll be shocked if he does not hold two belts, and not at all surprised by holding three.