I started this thread a while back, now I'm going to build a R129 road race / track day car.
http://www.peachparts.com/shopforum/sl-forum/313615-modern-post-50s-sl-race-cars.html
Found a ragged but structurally sound 91 300SL that is bad in all the right places. ( M103 24V with CIS, 5 speed auto 722.5 hydraulic shift ) The general plan is to remove the entire interior, yes dash / AC heater / seats / soft top , roll bar included. Every non useful part will be jettisoned. It will get a full cage so some weight will return. The side windows / hard top will stay because the car will still be street driven.
The general plan is to use the powertrain from my 97 E320 parts car as it is the same power train as my 97 SL320 ( M104 with ME FI , 5 speed 722.6 electronic shift. ) then develop it for possible transfer to the 97 SL320.
This build isn't likely to start in force until spring 13 as I have way too many other projects to clear out.
I'll be adding any progress / possible interchange questions from time to time and will likely start a interchange thread in the tech section since it gets better traffic.