Aspect Ratio changes?

Hey everyone,

so i am in a bind and would love some help.

I have a film im editing. I just spoke to my DP and he told me that the raw RED footage was shot at 1.9 aspect ratio and needs to be letterboxed at 2.39 ratio.

I have been trying to figure out how to do this without using an adjustment layer and cropping down so here i am asking for help.

so the image size is 8192x4320.

its easy enough to add an adjustment layer and crop out 132 bars on top and bottom, or 9.5%.

but i am really hoping there is a more professional and scientific way to do this.

any ideas of how to make this happen?

thank you in advance.