HDD switchers for PCs suck ass, as they take as long as 20 seconds to mount. My 0.02 on those...
You could use a Y-splitter for power and either a rotary switch (4 Pole whatever Throw) or 2 DPDT since you need to control both the 12v and 5v rails. Might need some extra wire as well (I think it's 18 gauge, but I'm not sure).

Sorry for the messy pic...

It doesn't matter if there's four or six "tabs" to solder the wire to.
One switch controls one drive while the other controls the second drive. just don't have both on at the same time.