I did a review a while back on the Pic Rail adapter (only works on the rifles with the receiver grooves, the "sniper notch" is not necessary). Don't think these are available anymore, so not exactly what you would call a plug for the product:
http://www.canadiangunnutz.com/forum/showthread.php/1131313-SVT-40-Picatinny-Rail-Review
I was quite concerned about shells bouncing off the scope when I installed this, especially with that particular scope with it's huge objective lens. But I'd also spent a fair bit of time watching slow motion video of the action of SVT-40 (poke around YouTube, there's a few videos floating around), and it gave me a bit of insight before I tested.
The shells on an SVT-40 leave the chamber at about a 45 degree angle, forward and to the right. It actually requires minimal clearance above the chamber for a scope to be safe from ejected shells.
I ran a few hundred rounds with the gun set up in the above configuration, and didn't have a single stovepipe, and not one shell dinged off the scope. They all ejected normally. sailing off into the distance forward and to the right like my rifle always does.
In the end, I removed the rail and left the rifle stock. Not because of any problems with function, but because I prefer the clean lines of my SVT without any bolt ons, and I shoot that rifle in competition from time to time in vintage class, and the rail would count as an illegal mod.
You should have no need of a deflector or high rings for good function. However, I will add the caveat that this is how things worked with
my rifle, and SVT's are a bit notorious for each having their own personality, so your mileage might vary.
Cheers.