Convert Mac Pro internal boot drive into an external harddrive without wiping

I have a 2008 Mac Pro running Yosemite. I just purchased a solid state hard drive which I want to become my boot drive. I do not want to transfer the data from the original boot drive to the solid state drive; I just want to be able to access the data on it.

Is there a way to move it to another slot and not have it run as a boot drive, so I may access the contents?

and/or

Is there a way to essentially turn it into an external hard drive, so I can easily access the contents?

Thank you