Is it possible to setup failover clustering between a 32 bit instance and a 64 bit instance?
Windows Server 2008 (no R2) did ship a 32-bit variant of the OS (last one MS shipped that way). So you can cluster it. You can install a 32-bit FCI on a 32-bit node. You cannot install a 32-bit FCI on a 64-bit node. So no, what you want is not possible. If you need a 32-bit FCI, install it on a 32-bit OS.