I use the Morley A/B/Y switcher and have not had any problems with it so far. It was only about $45 at Sam Ash. Be sure to get a A/B/Y switcher if you want to run both amps at the same time.

I use it for the setup you described. I run a Marshall JCM 800 into a 4X12 for the overdrive and a Marshall JCM 900 into a 4x10 for the clean.