Proper connector for cooktop

I previously had a range/oven combo. It was plugged into an outlet that was attached to the 3 wires in the above picture. The wiring is 6 awg aluminum and is on a 50 amp breaker. I now have a cooktop only that I want to power with the existing wires. The cooktop wiring has a red, black and green ground wire. The cooktop requires a 40 amp circuit but states that a proper AL/CU connector be used when connecting to aluminum wiring. What type of connector would you experts suggest. Any other relevant info is appreciated as well.

 

Do you have room to put an electrical box in there? IF so, you could use wire nuts approved for AL connections. Is there a provision in the cooktop to feed in a cable and make the connection inside of it? If you want a plug specified for 50A, one of these will work

https://www.grainger.com/product/49...82713&ef_id=WvCTVAAABKrwUjcG:20180510185856:s

 

I was planning on putting a metal box in there, attached to the back of the cabinet. I am just trying to understand what the best connector would be for this AL/CU connection. Thanks.

 

This is what you place on the wall with and then get a plug with the matching blade configuration. This is rated at 50 amps but you can change the breaker to a 40 amp. The second one below is another option that would be mounted in a electric box. If you notice the engraving on it is AL-CU, aluminum or copper wire rated.

https://www.homedepot.com/p/Leviton...h-Mounted-Single-Outlet-Black-05206/302480499