What is the end use / goal of this project?

What suspension / brakes / differential are you going to use?

What condition is the SL in? These cars are worth $$$ and it might be better to build a SL body from scratch on another chassis.

Other than making the engine and trans physically fit, the electrics won't be as complicated as some may make it out to be if you use all of the stock systems. Basically you need to make the engine / trans / computers think they are still in the CLK. This amounts to feeding the proper wheel speed to the ABS computer. In order to keep the engine computer happy a way to fool the evap test into passing or not running may of may not be needed.

With careful reading of wiring diagrams / shop manuals, you can discern what computer systems can be separated and what ones need to stay with the engine. Making something from scratch is a sure way to end up with a mess.

Another consideration is to do a SL body on a CLK chassis. Have a look at:

With minimal mods to the body, this still can be more or less viewed as a 190E
https://www.youtube.com/watch?v=sTgjWD7a67M
80's 190E body on C63 AMG Project
Channel CHERAL AUTO
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This car was stretched / widened / fabricated so far away from a 190SL I won't call it a 190SL, it looks more like a 300SL kit car with wheels that are way out of proportion of with the rest of the car.
https://mercedesheritage.com/classic-mercedes-culture/600hp-190sl-mercedes-bent
190sl amg sl65 Richard Mott