Mark, I finally located one of the dogleg gearboxes here in the USA, a rebuilt one from the correct BMW. For my car, I got the close-ratio box with the 1:1 fifth gear, not the overdrive. If the ratios are too tall once I get it driving, I will change the rear axle back to a 3.46 from the 3.27 in it, but I suspect they will be fine. I like the rev level on the highway with the car as it is: direct drive top gear with 3.27 axle. What I need is more closely spaced 1-4 gears so the engine stays revving. Hopefully this will make the car better to drive, as I have felt that the original four-speed's ratios are too far apart for the size and power of the engine.
I will PM or email you off line. I would like to order the kit you make which adapts the Getrag gearbox into the 113 chassis and mates it to the 280SL engine/bell housing..