Combines JD 6600 Add 4WD

If you consider the cost of repairing the field after you rut it up, I think it is easier to justify large tires than the 4WD. As a bonus, you get less compaction from the large tires even when it is dry enough to run without 4WD. We put large radial tires on a machine last year and then just turned the 4WD off. All it did was cut our ground speed down. I would think 30.5-32 or 35.5-32 tires on the front and 18.4-26 tires on the back would get you through just about anything with that size machine. If you can find them used, the price shouldn't be too bad. Just my 2 cents

Your combine has to be a hydrostat for the RWD to work. Yes you can mount it yourself, should have a heavy rear end though.