Yes, but the 20G would require a longer driveshaft (that runs between the PTO and the front axle shaft) than is used on the 8163. You would also need to find a longer 20G lift rod, or lengthen the lift rod used on the 8163.
Older blowers were 38" and 44". Older tractors with single cylinder engines can turn the rear wheels in and thereby accommodate the 38" blower. Your 20G (along with the 18G and 16G) can only have the wheels turned outward, requiring the 44" or newer 48" blower.
The 8163 can use any Gravely blower - 38" and a 44" Snow Cannons and 40" and 48" Ariens-Style blowers - so you need to check which blower it is before you'll know if it will fit your 20G