The P-38J by Revellogram is the old Monogram kit which is a bit of a pig. The ProModeler kit is an early variant, is licensed from Hasegawa and is very good. The Academy/Minicraft kit is also very good.
As for the natural metal and the panel lines, there are several ways to achieve both and all I can recommend is to try some or all techniques that you come across and see if they work for you. I have my favorite methods, and some of my pals prefer other methods. What works for me may not work for you.
For NMF you can use buffing & non-buffing Testors Metalizers, SNJ and Alclad. You can also use regular metallic paints and buff them either with or without a polishing powder (such as comes with SNJ). Or you can simply leave them as is.
I have a few methods that I've used for varying tones of natural metal, but I confess that I prefer to replicate a weathered natural metal finish rather than a pristine, brand-spankin'-new airplane.
For the panel lines you can use a wash, pastels, a pencil or pre-shading.
For a wash, thin out some black paint (or whatever color you prefer) and run it into the lines. Take care not to use an enamel wash over an enamel paint job! Some popular types of washes utilize oil paints and enamels; and though acrylic washes are tough to use sometimes, they can be effective.
One problem with acrylic or watercolor washes (I've used Cottman watercolors to great effect) is that the wash tends to bead up on the surface of the model and won't coat evenly. Some folks add a drop of dish detergent to their washes to break the surface tension, but I use tea as a base for my washes.
For pastels, use the hard chalk-variety (not oil pastels) and work them into the lines with a brush. Alotta guys recommend scraping the pastel into a powder, but I usually scrub some off of a block or a stick with the brush. It's more simple and just as effective. Also, you have a bit better control during application that way.
The type of brush is up to you, but my faves are called "cat's tongue". They have a shape similar to a cat's tongue (thin cross section, but a broad face with a rounded tip) and are also similar to another type called a "filbert", which is usually much more full and "puffy".
You can use a pencil to highlight panel lines as well. Either use a regular pencil with a very sharp tip, or a mechanical pencil. I prefer a .03mm mechanical 'cuz it doesn't need to be thinned down for most panel lines. There will be a sheen to the lead when on the model which can be knocked down by a flat cote.
Pre-shading is usually done with an airbrush and entails painting over the panel lines with black, or another dark color, and then applying the paint job over this, allowing the black to show through slightly. The degree to which you let it show is entirely up to you. In several ways it's a better alternative to using pastels or washes, but the technique you use is up to you.
Try these and other techniques out and decide for yourself which you like. And practice, practice, practice! I have several "testbeds" that I use to test new techniques or simply for practicing if I'm a bit rusty.
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