The rocket tubes on updated models are located inside the aircraft bitmap now.
For the P38J, when looking at the default texture, it's located in the darker green area below the red NO STEP area and above the vertical stabs.
You might want to try creating a temporary 'mapping' layer over the entire bitmap with various colors, numbers, letters or grids. This allows you to pinpoint which 3D parts correspond to what area on the 2D bmp. I'd post the layer that I use for locating the texture map, but no hosting is available. PM me your e-mail and I'll fire it over to ya.
