You are going to be looking at all the same things as you would a regular 2x4 van, with a few exceptions. The VC's should be checked as well as lockers if they are in place. Look for vans which already have some of the expensive upgrades done if possible, especially engine conversions (if you are into that), big brakes (if looking for a camper) and suspension. Everything else is pretty easy to work on, save front hubs.. they are made of unicorn tears and can be very difficult to find. Luckily, they rarely blow out, especially if you are good with keeping up with the wheel bearings.
Like any "old van" there will be gremlins to sort out, but everything is workable and most parts are available through a surplus of aftermarket dealers.
One thing that is very true with Syncros is that you often get what you pay for. Most of the "amazing finds" have been long found and there are a number of overpriced rust buckets out there to be had.
Best of luck with your hunt! I love mine (and its for sale).