Yes the stage 5 have a very big reservoir. I have 1.5 inch wheels spacer each side and all fit very well. I think without the wheels spacer the shock don't fit except if you put the reservoir inside.

Wow, if somebody gave you a set of rear Elka stage 5 shocks for $300 then you have a good friend there.

Yes !
I have call Elka today and they said my spring (225 lbs) is ok for the Z !
I can add one more 2 inch softer spring (150 lbs)for better low speed comfort and 1 more 3 inch stiffer spring (350 lbs) for prevent my rear to not drop to low because of the add travel.
I have 2 times the stock travel now ..

Interesting, I just heard back from Elka today & they have an application. I will dig into it & post what I find.

Go directly to the Elka Canada site.
All is there with the price.
All stage available

Doesn't appear to show listings for the Trail/50" model. Just the EX and the Snypers.

[2015 Z Force 800 53/Trail EPS]

Doesn't appear to show listings for the Trail/50" model. Just the EX and the Snypers.

It does. They are listed as just the ZForce 800 without the EX near the last pages. Found them on the stage 3s and 5s.

I have confirmed with Elka this morning and my spring is the good one. All Elka for the ZForce 800 trail have the same spring.
4.0 x 254 (225 lbs rate x 10 inch)
It's the same spring for all stage 1-2-3-4-5 and all stage are available.
I will try to post pic of the shocks on my ZForce tonight.

We can do the trail model (see attached SXS application)

Use the CF moto Zforce 800 2015 (p.7/14)

http://www.elkasuspension.com/

This is from my contact @ Elka.

I have 2 times the stock travel now ..

If that is so, and I'm not at all suggesting it isn't, I have to wonder why on Earth CF Moto would select a rear shock that causes the SXS to have half the suspension travel than it could/should have, and then fit it with a teeth shattering spring that's already made coil bound for fully 2/3 of its length when the machine is sitting level and unloaded!

Did they let the janitor try his hand at designing some operating specs?

[2015 Z Force 800 53/Trail EPS]

Does look like they would spring-bind before the shock travel ends...wish I or someone could get the full swing measurement with and without the shocks.

Yes, with consideration to staying within CV joint bind limitations. That would be interesting.
Can't recall the values right offhand but I noticed at a recent ORV show the Can Am Maverick 50" model advertises a lot more rear (and front) suspension travel than the CF Moto and both have A arm suspensions.
BTW, found the Elka listing, thanks.

Same here, I don't understand why the travel is so limited on stock set up. Remove your shock and you will see that the wheels can go A LOT more high without any trouble with the axles.
With the ELKA you can use all the space under the fender. I don't know if it's to much but the ride is 10X better. 
I will add a 2 inch bracket to put my 20 inch shocks to 22 inch long so I can take advantage of all the wheels travel of this shock set up.

With that little modification my rear set will be exactly like I want.

The front suspension are a lot more limited by the axles.

Is there any way to buy just springs to replace the ones on the cfmoto shocks?

Here is a few pic