I'm pretty much in agreement with Steve on the CK30 being something that will impress you.
I love to work with old tractors, and have a working familiarity with several of the the old Fords, Olivers, Masseys and ACs from the 50's and early 60's. I wouldn't consider my self an expert, but I've used several and restored some too.
The CK30 will easily outwork your NAA. HP will likely be higher on the CK30, which is a 30hp tractor largely because many of the old gas farm tractors are no longer producing the same HP that they were rated for when they were made due to compression losses, and a host of other factors. If the NAA was still giving you something in the upper 20's range you'd be under the CK's HP by several HP. I suspect, without bothering to look up a torque curve on the NAA's engine, that the CK is going to offer more torque than the NAA all across the range. The NAA will have more weight than the CK so you might notice the CK pulling harder with the box blade, but you might not. And the CK will have 4wd working in its favor so while it won't have the rear wheel traction of the NAA, it will likely have similar overall traction. Unless that box blade is 6' or wider, you should not have any trouble with it, and you might find a 6' box blade will pull OK? For the other implements you mentioned, the CK will easily handle everything you already own.