Given that your choices include a gun with a carbine mag and one that's a Mk23 pistol in a body-kit, I assume that a .308/7.62mm style magazine isn't a deal breaker for you.
In that case, you could just up-spring your SSR4 and restrict it to semi with a grub screw (depending on your local site(s) rules). A barrel extension and/or silencer can let you use a longer barrel, and swapping out the cylinder for an unported one is simple enough if you want to open the gearbox.
If you want something new, magazine cost and availability needs to be factored in. The Vorsk only uses its own proprietary mags, and they're not cheap, nor necessarily available (PatrolBase doesn't have any long mags). The SSX303 (which is non-blowback, not blowback) takes Mk23 mags, which gives you more choice. If you want to go gas, I'd go with that over the Vorsk all day long.
The East Crane (who?) and Golden Eagle will both need locking to semi, and up-springing (same as your SSR4 would). Both use proprietary low and mid caps, so again you'll need to factor in cost and availability to buy more.
The Double Bell is the only AEG on that list which is actually "DMR" spec out of the box, and comes with a hi-cap magazine so there are no extra costs. I believe that mid-caps are available. I'd be looking for reasons not to get that from those 3 electrics.