It's been too long and my memory always did suck...
Didn't have a windlass on our '87 Mk III... I don't remember what chain we used...
But I do remember a 35-lb original Delta anchor didn't always do so great here in the Chesapeake mud. And a relatively small (~14-lb?) steel Danforth usually worked like a champ. There are boatloads of "new generation" anchors to choose from that would likely do better in our conditions. Any one of those, plus a slightly oversize Fortress, might make a decent combination. (Our current primary is a SuperMAX, but you can find good reviews on about 6-7 other likely candidates, some with multiple choices: Spade, Mantus, Rocna, Anchor Right, Manson, Ultra... probably others I'm forgetting.)
Generally a windlass gypsy will work with a specific chain size for proper function.
Some windlass units have a rope/chain gypsy (i.e., a single that functions with both), and even an extra capstan for rope. Our current Maxwell RC 10/10, for example has a rope/chain gypsy, and they also offer an additional capstan model to handle two separate rodes independently -- as for a second anchor, etc.
-Chris