Anyone here have a CZ Scorpion and know if the model year makes a difference?  I'm seeing 2016 and 2017 and not sure what the difference are.  I'm planning on buying the pistol to okay with while the form process to convert it to an SBR.

Also, what mods can be done while it's still in pistol form?  Is the only that really matters the folding stock or any kind of stock if it's not an arm brace?

You probably ought to check in at what might as well be called the CZ Scorpion forum.

https://www.ar15.com/forums/f_6/48_Pistol-Caliber-Carbines.html

Hahaha, thanks!  Hadn't seen that section before.

To answer your question, you cannot make it an sbr without approval first. So, no you cannot add a stock to it, but you can add an arm brace and any other parts you want.

In case you're still wondering, here are the differences by year, from what I can tell:

2015 = plain sling slot backplate, 18x1 barrel threading, non-welded trigger pack screw
2016 = QD socket backplate, 1/2x28 barrel threading, welded trigger pack screw
2017 = QD socket backplate, 1/2x28 barrel threading, non-welded trigger pack screw

There was also a very slight change in the magazine release texture/shape sometime in early 2016, but the difference is negligible.

I'd recommend a 2017 production Scorpion.  The backplate isn't that big of a deal in the long run, since you're going to be swapping in a stock eventually.  But the more common 1/2x28 barrel threading makes attaching muzzle devices or silencers easier, without requiring an adapter.  And the non-welded trigger pack screw means you don't have to drill out and replace the welded screw in order to swap springs/triggers/etc.  (It's not hard, but it's annoying.)

Except for a vertical foregrip.  Per the ATF, vertical grips are a no-no on a pistol.  But angled foregrips are fine.

Save the stock and the vertical grip for after the tax stamp.

Yeah, forgot to mention the VFG.
Interesting observation about the year models. I guess mine was a really early 16 model, I got the worst of all of them. Non QD backplate, welded trigger pack, AND 18x1 threads.

I'm pretty sure you can not put a vertical fore grip on either. Last i read, a vertical fore grip on a pistol is a redesign that null and voids the "intended to be fired with one hand" part of the atf definition.

I'm in the same boat with you but I haven't found the thread pitch to be a problem. My Omega 9k is on it via direct thread SiCo mount and it never comes loose. I don't really swap the can much at all either so it's a nonissue.

Go with HKParts if you opt for a 3-lug silencer mount.  It is designed to work on both metric & English threads, & has recesses to accommodate the FH tab.

The back plate QD mount is irrelevant if you will be installing a stock.  Get the PMM QD mounts the install on the factory hook loop mount.

2015 model w/ 18x1 threads and non-welded trigger pack.  Prefer the 18x1 threads because the thread mounts fit closer than the versions with both 18x1 & 1/2-28 threads.

This is a little different take on the topic but I have had a CZ EVO for about a year and a half. The only mod I did was add a brace tube and a small red dot. This thing is awesome and there is no ATF paperwork needed. My buddy just bought a new EVO with the MLock type hand guard and SB tactical side folding brace. Amazing what you can get now a days with the braces. These feel and shoot amazingly well with all ammo from 115 to 147 so far with no malfunctions. Even the mags have been perfect for me.  I love being able to see how many rounds are in there. It is such an awesome little gun that I want another one for no good reason.The regular sights are fine but it is so easy to mount a little Bushnell up there I don't see how you could have any regrets buying one unless you really are in love with HK MP5s in which case you will wind up buying one at some point anyway. Did I mention that the CZ has a BHO on last shot and is easy to mount optics and lights and the such.