79I is interior trim. 799 is seat belt color, 79B is for your cloth, apparently. Sometimes they use a C, sometimes a B, not sure what the difference is, I haven't dug that deep into the breakdowns. May have something to do with the material going on what seat type, I am not sure. I might dig into that one day. But not right now.
Now, xxU and xxL (two number paint code for the x x as an example) are upper and lower exterior paint colors, if used. so xxL and xxU would be for exterior paint colors. You have 15U, meaning medium gray metallic paint all over.
Since it's a supreme (GR47 in the VIN), those buckets didn't come standard in it. In fact, A65 tells me it had a cloth front bench split with folding armrest.
Basically, everything inside should be dark claret, aka maroon. Go with 1986 code 79. They'll know what to do.
N33 is tilt wheel, A01 is tinted windows all around, C60 is A/C, and LD5 is 231 V6, and an MV9 TH200 3 speed, with lockup tc. All through the 2.41 gears, GU1, in a G89 7.5" rear out the back.
N67 14x6 chrome SSIII wheels, black inlay, and QMX P195/75R14 BW steel belted radial tires.
UK4 AM/FM stereo radio, with seek and scan. Plus the VK3 front license plate bracket.
But that's pretty much it. A sparsely equipped Cutlass. But nice looking, nonetheless.