Researching this a bit, can't seem to find any examples of mating an SCR with a left handed upper.  Has anyone tackled this, either with rear or side (preferred) CH?

I have an SCR and I tried and failed to create a left-handed upper for it. It's possible, with the right hard-to-find parts.

The SCR uses a standard bolt, but with a proprietary carrier with the rat tail that curves down into the stock during recoil. This is why you can do caliber conversions which only require a bolt change (300bk, 6.5G, etc)

The Stag lefty uppers are a mirror image of right uppers with a left-handed  carrier. From my research it won't work on an SCR because the bolt itself is standard and the gun relies on the lefty carrier to position the bolt 180° from standard to eject out the left side. Placing the Stag bolt in the SCR carrier would still resilt in ejection out the right side of the gun. Some say you also need a left handed barrel extension which has the lugs chamfered on the other side because the Stag bolt rotates the opposite way, but others say this is a non issue.

DPMS made a Southpaw upper which achieved left hand ejecting with only a proprietary bolt. The front and back of the carrier are not in normal allignment but have a half turn down the middle which let it fit in standard carriers, but had the bolt face the correct orientation to eject out the left side. With this upper and bolt only this should work with the SCR carrier, and correctly eject out the left side.

I looked for about a year and was only able to find 2 compete DPMS southpaw rifles, and I didn't want to buy $1200 complete guns just to strip them for their upper and bolt to use in the SCR, so that project died.

Feel free to PM if you have additional questions.