You can remove one of the drives, install 8 on the other, and then remove the one you just installed on, place the other back in, and then install 8 to it. You will have 2 totally independent installs, each of which boots from its' own loader. This was the situation for me not too long ago, I was using TrueCrypt whole-drive encryption, and wanted to be able to encrypt both Win8 and WinServer2012. But a limitation of TC is that you cant have 2 encrypted Windows OSes on the same drive. So I did the above and it worked. I just had to use the Esc key to choose which drive to boot from. It probably could have also been accomplished by installing a custom loader like GRUB/GRUB2, putting entries for each Windows OS in there, and another entry for Linux. In my case I was using 2 HDDs instead of HDD/SSD combo, but it's still the same process regardless.

You can also have one Windows OS on one drive, another Windows OS on the other, and simply have them share a bootloader. I'm not sure how this would be done, but I think you can just designate the 2nd HDD/SSD for the 2nd Windows install, and it should still recognize the bootloader on the first drive and use that for booting. Just set the SSD as the first bootable drive in the BIOS and you will be able to choose between each after powering on.

A third option is to install each OS into its' own partition, without the System Reserved partition, which from what I've read isnt absolutely necessary to have unless you plan to use BitLocker. This will give you one partition per drive, one for each Windows OS. I've found this useful because I like to run Linux as a 3rd OS, but there is a limitation of 4 primary partitions for a drive. System Reserved counts as one primary partition. So I usually install without it. This can be accomplished by creating one partition on each drive BEFORE installing the OSes, formatting each as NTFS, and then using a command line util like DISKPART to set each partition as active and with the boot flag. This can also be done in a Linux util like Gparted, by booting into a live Linux USB distro and running Gparted from there to do the steps above. This forces the installer to place Windows into only the one partition without System Reserved. The boot files will be on the C drive itself. I've studied up on this and it has no noticeable negative effects, you can still use things like System Restore, Refresh, etc.

To boot to either the SSD or HDD just set one as primary in the BIOS, and then use whichever button your system uses to select the desired boot drive. Each OS will have a C drive no matter what and that generally cant be changed. But, from within each OS, you can still assign another drive letter to the other OS. Each OS will still see itself as the C drive no matter which one you boot into, no issues there. It has also been pointed out that each 8 OS cant be activated with the same Product Key, you will need a different key for each. You can have as many Windows OSes installed as you want on one machine, the only limitation being the available amount of space, and each must have its' own key. Microsoft will not give 2 sh*ts about this as long as each installation is duly licensed.

A question though, and this is a problem i've had in the past, is that if I try to install 8 without removing either drive then Windows will be installed to whatever drive I selected, but the installer places System Reserved on the other drive (not a partition on the same drive, but on the other physical drive). When I install with one of the drives removed this doesnt happen. It doesnt matter which drive I set to boot first in the BIOS, this always happens. Each drive is identical and the same gigs size. Why does it do this? Any way to install normally without removing drives?

Hope that helped!