Silvretta Easy Go 500 Adjustment?

I'm putting together a new approach set up - Silvretta 500s on a new pair of Altai Hoks. I have them mounted, but having a hard time getting my old Scarpa Invernos in the bindings. The "welt" on the heel is too high up. 

Looking at where the metal bar that supports the heel component contacts the bottom of the heel plate, you'll see that it attaches just off center. It attaches to a grey piece of metal that looks like it should be able to rotate inside the black plastic circular groove  (red arrow for reference). If I could rotate that grey piece 90 degrees clockwise, it should place the point where the metal bar contacts the heel plate higher, the top of that circular groove.  

This is all a guess based on a frustrating evening of tinkering.  I don't know for sure if that grey piece rotates.

Does anyone know or have a picture of the binding's manual/instructions?

I wish I could be helpful.

I acquired some skis with those bindings on them.  They fit on my nepals okay.

FWIW, I was messing around trying to get the bindings to release and got that piece to rotate... my best guess is that this is part of the release system, as it did rotate when popped the boot out.

What does the screw under the gray cap at the top of that heel piece adjust?

I'd be a super stoked if anyone has a manual, as I certainly am a noob when it comes to ski bindings.

That is part of the release mechanism. As I recall a lateral release will rotate those smaller grey pieces which ultimately releases tension on the rear bail and the boot can release from the binding. If you pull the heelpiece sideways you should see it happen. 

Silvrettas fit most but not all welted mountaineering boots. I had a set of AKU boots that were basically LS Nepal copies that did not fit, although the Nepals fit great. 

Linnaeus wrote:

That is part of the release mechanism. As I recall a lateral release will rotate those smaller grey pieces which ultimately releases tension on the rear bail and the boot can release from the binding. If you pull the heelpiece sideways you should see it happen. 

Silvrettas fit most but not all welted mountaineering boots. I had a set of AKU boots that were basically LS Nepal copies that did not fit, although the Nepals fit great. 

I see, you're right. I was applying lateral pressure last night to activate the release and didn't see the grey piece moving. I just now did the same but with some twisting pressure and it moved.  Thanks for the info.

Now I just need some new boots apparently... bummer...

This might be dumb, but if you slide the rear part of the binding farther back, would that change how thick the welt can be?  Like, if the hinge is closer to the rear of the sole, it might increase that height, given the bent-ness of the rear bail.

Looks to me like you are maxed out on length. You should be able to get those boots in a Silvretta 500. You just need a larger size binding. I think they made three different sizes.

Just wanted to follow up.  My buddy and I got the boots to fit.  I had to adjust the heel DIN setting a bit using the screw below the gray tip that you, John, mentioned, and apply some more muscle to get it in.  I'm at a DIN setting of 6 and things feel solid without feeling forced.  Chalk it up to a non-skier not knowing what he's doing.  :) Glad my buddy skis and knows a thing or two.

Thanks for the input everyone.  Looking forward to getting out in the snow this winter.