Carnera was 6ft5 and 250lb? Add another 7 inches of height and 50lbs of weight. It could be like comparing Choclatito to Kovalev.
You'd probably have to punch him with your back against the ropes and hope he falls backwards. If you punch him in the middle of the ring, the ropes would keep him up.
Primo Carnera had a famously fragile chin. His own manager described Carnera's punch resistance as follows: "Primo couldn't take the lightest punches. If he was lightly tapped on the chin by a 50 lbs lighter man he would hit the floor. It was a shame". His own manager! Regarding Valuev: He only fought handpicked cans, won robberies vs. Donald, Ruiz and an ancient Holyfield and looked like a clumsy oaf vs. Haye. Anyone with a pulse would knock the living daylights out of him. Heck Wilder would send him to the ER.