Continuing on with what Gilmourisgod is saying, I'm not sure why you would need a template. If you are making an aluminum pickguard, you aren't going to be routing it (I hope!) with a template.
Use the existing pickguard as a pattern to scribe the external shape and pickup opening onto the aluminum. Drill the holes, and use hand tools to saw and file it to shape. It's not hard.
Here's a thread I wrote all about making aluminum pickguards:
I occasionally get asked to make up brushed aluminum pickguards for my clients. I happened to be doing one yesterday for Keith Horne, for one of his 10-string basses. So, I decided to document the whole process here, to encourage any of you who are thinking of getting into your own metalworking on your projects. Custom metal hardware can add some real class to an instrument.
Making pickguards or control plates from aluminum plate is really pretty simple, and is mostly done with hand tools. The only power tools I used were a drill press, a bandsaw, a stationary belt sander and a bench...