...Haven't been active here in years, posting this to hopefully help others. I've wanted to do the RichardSohn OMP adapter coversion forever, but they quit offering the option for the S3 13B in the GSL-SE model many years ago. Last year, out of the blue, I discovered that "Sakebahn Classics LLC" was finally offering a version for the GSL-SE. So I bought it, and couldn't find any info on anyone else doing this specific conversion. So I made it up as I went, and thought I'd post what I've done to hopefully help someone else attempting this install.
First of all, to make room for installing a 2 stroke reservoir, I found out it was really easy to relocate the charcoal canister off teh strut tower to where the useless sub-zero starting assist reservoir is. I removed the sub zero tank and installed the charcoal canister there. That involved removing the charcoal canister by lifting straight up, off it's mount. Then removing the two 10m bolts from the charcoal canister mount and then cutting the bottom ~1.5" off the bottom of the charcoal canister mount so that it could be mounted in place of where the sub zero tank was. Then the charcoal canister could be squeezed and mounted under the cruise control mech where the sub zero tank used to be. This then opened up the area near the strut tower for the 2-stroke reservoir. For the moment, this is just a mockup to prove it works. But if I'm honest with myself, I'll prolly never "beautify" the installation or care what it looks like. Much like when I went DLIDFIS and created a working system, but never made it look nice...
One big note on the Sakebahn OMP install in my case, if you still have the air pump(I do,but it's gutted and just a glorified pulley to help with belt slippage at high rpm.) then you should really shorten the oil line input brass barb on the OMP adapter as it sits RIGHT under the air pump mounting bracket and is a REALLY tight fit with the oil line there. Wouldn't be a concern at all without teh air pump bracket being there, but if it is, do yourself a favor a get a shorter inlet brass fitting.
I did this conversion this past summer and have driven a few hundred miles with it. I am very happy with the outcome of the mod. My car doesn't backfire anymore,smells better, seems to run better. Very happy with the conversion. BTW I also rebuilt the factory OMP with "Atkins Rotary" rebuild kit. ALSO, I got the headlight bushings from "Sakebahn Classics LLC" and they were amazing. I've never heard/experienced quieter operation of FB headlights...Ever.
Here are some pics of my install, hope this helps someone...