Not a great combo - the 27" is 82PPI, the 19" are 89PPI. That means if you treat the layout as a SLS it won't line up very well.
If you're just going to game with it then it doesn't matter because neither nVSurround no Eyefinity supports PLP, so you'll only be using the 27" monitor anyway.
I don't want to dig up the posts on my tablet atm, but if you search my nickname and 19" sidebar you can find some posts I made about this. I have such a setup, with the 19" set back a bit and angled inward slightly so that their ppi and bezels match pretty much. They work great as "sidebar" space for chat, progress meters, download managers, email index, playlists / music streaming svc, simple text documents/referencing, etc. I have two full size monitors in the array as well - a 2560x1440 60hz ips for all things desktop, and a 1080p 120hz for gaming. I do not PLP game at all, the 19" ones are sidebar space which are very useful for text based things/lists/simple readouts and progress meters, etc.