I think you will find the slide is on the outside of the assembly, and as the slot runs through to the inside, it is open to the light so to speak. I pondered for ages trying to work out how to keep the slider as is, but realised it couldnt be made light tight, so inside it went, with the old slot being filled in with the felty stuff (its good) Also this move meant I could reverse the helical because the back had a better area to mount a lens plate onto, and it makes no difference. Its only the inner moving part that is reversed, the lens outer parts are the right way round because they offer 3 screw holes to fasten the whole thing onto the camera. I maybe cant make this too clear! (its hard with words and no pics) but the only part I chopped up was the inner moving helical, and as you will see apart from a few gaps to fill and make light tight the outer part with the focus ring needs little work apart from the new slot thingy. I'd be interested if you come up with a different solution to what is a pain in the arse to figure out!
I think you will run into similar problems as I had, with the slot/light tight issue, and the only way I could work round this was to put the slot in the dark, inside, with a reversed inner moving helical, and as I said it all works a treat.
Steve, the only thing in doubt here is wether your 65sa will fit the 'hole', as I mentioned the 47sa is smaller, and the 65 angulon posed no probs at all. If you have access to some metal removing machinery you may be in a good position. I only have a Dremmel.