Wintec 500

The number and length of billets should give you a definitive answer.

I have a 250 AP and it has three short billets. The 500 AP should be the same way.

The 500 dressage will have two long billets for sure, regardless of whether it has a short center billet or not.

It has 2 long billets so there's my answer for sure :)

Your second picture is the older model. Wintec changed their tree and panel designs - last year I think. Top pic is the new dressage design as others have said :)