The 8Ns I've seen didn't have a differential lock.
Comparing the Nebraska tractor tests, the 8N weighed 2717 lbs unballasted, with 1582 lbs of it on the rear tires. A Yanmar 336D is 3405 lbs unballasted, with 2050 lbs on the rear tires. Both machines make comparable power, the 8N peaking at 21.95 drawbar horsepower, and the 336D at 22.46 hp in 2 wheel drive.
I think that is about as equivalent as one could ask among machines that are of different design, manufacturer, and generations. I'd look for implements sized to fit the 8N, the Ferguson TE-20 and other similar machines. A 5 foot disk or box blade and 2 bottom 12 or 14" plow (or the disk plow equivalent) should work very well for you, and you should be able to pull them at any reasonable speed with the implement ballasted, if need be, to get proper results.
A 5 foot rotary cutter should be easily handled, and you should be able to power through virtually anything. Other implements should be fine at wider sizes, depending on what you're doing. With the Yanmar machines you have the advantage of using a tiller easily and well.
One thing I have noticed in going through the Nebraska test library is that all of the tests involve tractors ballasted with amounts of weight that are generally unreasonable to achieve for the average person: The YM240 test had 430 lbs of cast iron weight on EACH rear tire, plus liquid ballast.
Car Doc has some harmonic dampers from some massive engines (I don't recall what offhand) that I think weigh something like 350 lbs apiece. They are massive (and awesome!) but still hang out a good distance from the outside edge of the tire. There is no way 430 lb weights on the smaller YM240 would fit cleanly, and weights like that are very hard to find, and handle. The 8N was tested with 450 lbs of iron weight per tire, plus another 217 lbs of liquid ballast in each.
The Yanmar's weights were far in excess of what the operator manual allows, and in contradiction to its requirement that only liquid or iron ballast be used, not both.