I know there is a lot of talk around the issue of the 400 being pretty attachment specific. So I have committed to build attachments for mine as I need them. Working on mine to restore/modify/accessorize it, I basically consider that it will have virtually no value when I'm done. But it will be a nifty and useful garden tractor for ME. It's a hobby that will cost some money that I won't get back. But it is a hobby that will get the lawn mowed, snow removed, shoreline rocks reset, firewood hauled, and landscape projects accomplished. It will tow the grandkids and neighbor kids on a hayride. My fishing boat won't do any of that and it doesn't catch fish, either.
All that said, the 400 is a pretty good platform to start out. The deck and blower are a good start. That's what I have. Then you add a 3pt hitch and (other than tiller) you have many options. At any one time there are a number of them being parted out on Ebay. I've found some parts there. Other that Deere specific parts, many parts are generic enough to be found elsewhere on the internet.
A 400 is a big and solid performer-worthy of a re-power if you can get it cheap enough and the Kohler is bad. I like mine. It's getting a combo box blade/land plane and a front loader that I'm building. Go for it!