I'd say it should, used to be used for rotavating and peeping spud beds, mainly ploughing now, was on the farmers journal last year ploughing with the 939, it's on the new low loader at the minute.I’d put the 8400 on it, love those tractors, just make sure the 1000 pto is able to run at 1070 rpm as thats where the JF needs to be, some of the big american tractors will limit revs as so that the PTO will not do anymore than 1000rpm. You want plenty of torque with the 5 blade drum and there is no replacement for displacement.
but in truth, any of those tractors will be fine, the setup of the harvester will make up for power, blades need to be set tight to the shearbar (<2mm) if they are any further back than that, you are just dogging the harvester. You’ll burn more diesel, make more noise and reduce your blow.
Might go down this evening or tommorow if yourmans not busy and go over the belts and chains and check the shear bar for wear and set it, aren't they double sided on the jfs, I know the blades are notoriously blunt on it so may sharpen them, is there a stone on it or do you have to do them all one by one. That certainly could be the problem.