A postcard template for you
Personally, I only work with CMYK elements for projects like this. I like to control the conversion from RGB to CMYK since I can to tweak the final colors in CMYK. You can control the rich blacks, ink densities etc.
Make the artwork (including bleed) and the Draw file the same size. I include trim lines inside that artwork too. It assumes the final trimmed size is 5.5" by 4.25". The reason I work this way:
A. There's never confusion over what the final trim size really is
B. It's very easy to tile the artwork at the printer end with trimlines inside the bleeds
For small jobs like this, I save the file. then I convert all text to curves before making PDF. Then make PDF. Then Ctrl+Z backwards to get text back, or close file without saving. Why? fonts will never be a problem this way for the printer. or you can use my handy macro for this.
Open the attached and see both pages.