Putting the junction box in the cabinet above or below is typical. Any box can be used as a junction box.

 

The top right is where the junction box should be located. You will need to raise the wiring to that location.
Unfortunately it looks like you have a finished back to the cabinet.

 

The top right is where the junction box should be located. You will need to raise the wiring to that location.
Unfortunately it looks like you have a finished back to the cabinet.

Yes, I'm going to have to cut the cabinet and drywall in order to move the wire to the location of the red dot in the photo.

There is only 1+5/8" between the back of the cabinet and block so I don't think there is enough room for any type of junction box behind the cabinet. I believe my only option is to put a junction box inside the cabinet. I'm wondering what is the best type of junction box for this that would hopefully be able to be secured to thin cabinet paneling?

 

The installation instructions will show where the junction boxcan go. You also need a connector on the flex conduit.

 

Just use a 4”x4”x1.5” metal box with a blank cover and let it float on top of the oven.

 

The box doesn't need to be behind the oven. It can go on top where the cutout is.

 

What's the appropriate size wire nut to join these? I also need to add a ground wire to ground the metal box, correct?

The aluminum wires from the back of the oven are 12awg stranded. I forget the gauge of the wires coming from the breaker. It is what is standard for a 240v oven.

 

Wirenuts are sized for the number and sizes of conductors to be spliced. What sizes are you dealing with?

 

The aluminum are 12awg stranded. I don't know the gauge of the wires coming from the black sheathing. I also think I need to add a 12awg solid to the ground wire nut to ground the metal box.

 

Use big gray or blue

 

I hope I can get 4 of them in that 4"x4" box.

 

The oven conductors are not aluminum. They are tinned copper. Use a deep box.