I heard of stories of people not being able to or having a difficult time moving the shifter left to engage reverse. Stories of having to use both hands and leverage to move the shifter left. I'm curtain this is the reason for the modification Stan does as part of the invert.
You may want to ask Stan or one of the Porsche transaxle experts about your specific issue.
FYI and in the case you want to try it directly from the transaxle...
If you're looking at the box, from behind the SL-C, during the shifter movement it will be a CW rotation and then aft on the shaft. Just like 1st gear, just with another degree or two of CW before the movement aft.