Or get an ER collet holder to use in place of the drill chuck.
I've not seen a stubby drill chuck with an R-8 arbor. Some are shorter than others, but they still eat up space. The collet holder is your best chance to shorten things up. Lengthening everything up to match your longest holder is another option but I wouls not advise it. Always run your end mills as short as possible. Always. (unless you are using them as a drill).
Scott
Consistency is a good thing....unless you're consistently an idiot.