if this is true, and I hope it is, then what kind of WMDs would they have been?
Most likely chemical mostly, from what has been said of Saddam's prior programs. The biological program was there but bioweapons are tricky to use so they're usually of lesser importance, inventory-wise.
His nuke program was there, but he wouldn't have had much but the experimental facilities and research documents.
Even the chem weapons would probably have not been a huge inventory. Its not the sort of thing that you really want to have a whole lot on hand at any one time. Logistics can be a bugger. And there's a shelf life on that stuff too. So it might be in the hundreds or low thousands of shells, but not tens of thousands.
Much of the stuff taken to syria could be raw materials, production equipment, documentation... That sort of thing, in addition to whatever inventory of ready artillery shells or whatnot that they had on hand.
Just a guess tho.