The Franklin Armory BFSIII HK-C1 Trigger - Binary Firing System for HK 91/93/MP5 will work with the Magpul SL Grip Module. You should not need anything else.
The Franklin Armory BFSIII HK-C1 Trigger Will fit most HK 91, 93, & MP5 variants and clones. Some firearms may require additional fitting but will still be compatible.
I recommend the ejector kit from Zenith. As you will need an ejector unless you remove the one from your existing grip module.