Pagz, if the early C36 is like the old merc's (W201/W124's) It's a piece of cake to bypass the trans. There is a 5 wire plug that goes into the shifter: Two small wires go to the backup light on the shifter. The other three go to a relay: The large and small wire's that are crimped together go on one side with the big single wire on the other. Then run a switch to either your clutch pedal or a switch on the dash (what I did). Pressing the switch triggers the relay and the car thinks it's in N or P which allows it to start, and has the N/P rev-limiter. Once's it's started you can take your finger off the switch and she'll run like she's in Drive. So far 15k trouble free miles on my setup that way. Also serves to be a bit of a theft deterrent since my switch is under my dash, so only I know how to start it
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As far as the LSD thing goes, apparently the Nissan S13 backplate is close to our merc's and the GTR pumpkin can be put in with it. Just get some half shafts and be done with it, or use ASD shafts and have some adapters made. I'll be trying this soon when my 201 goes FI.