Some old ones it's more difficult to get parts. Ford makes some parts for the N today and there are aftermarket parts. And many to be cannibalized.
The Jubilee was the last and being the Jubilee it was more robust, physically bigger, overhead valves, distributor on the side, and the clutch did not need to be engaged in order for the pto to function. That aside you can work the heck out of an 8N every day. Personally I have an affection for flat heads, they got the look and it's all iron.
Those Olivers were beefcakes.