Oh dear...........
Neither of these offerings would interest moi.
In my opinion, the 646 has been subjected to a lot of work since it was new and I'm talking about HOURS put on the tractor. The paint job is disgusting and was done for one purpose only........to disguise what the tractor really looked like. As noted, the original 15" rims are now gone because the owner is too cheap to put replace the worn out ags. It was more expedient to stick a pair of turf tires from a 400 onto it so that the tractor would appear to not need new rubber. WRONG. For loader work in off-road conditions, the Ags are a necessity. This guy was too lazy to mask off hydraulic lines, the Onan engine and other items that should not be painted. He couldn't be bothered to paint the back side of the rear rims. This is an example of putting lipstick on a pig at it's worth. If I was in the market for a 600, I would far sooner have an untouched example over something that has been screwed with like this one has been. I'd pay this guy $1500.00 perhaps but only after I took a really hard look at everything else on this tractor because when someone does what he did, that's just an indicator to wonder what other short cuts were taken and what else he is trying to hide.
As for the 644..... that one disgusts me as well. It's similar to saying. "Hey, I have this Shelby Cobra that I was going to restore but have now lost interest in. Here is the body and frame I'm selling for $50,000.00 but I'm happy to work with the Buyer and sell him stuff like the engine, transmission, radiator, windshield, bumpers, driveshaft, seats, dashboard etc to help him complete it." Wow......what a nice guy. Wow... what a deal. Gimmeee a break. Whatever you have around that BELONGS to the 644, put it ALL in milk crates and sell it with the tractor. Other than that, stick the tractor where the sun don't shine.