No.
Hardware Requirement
The two units in a failover configuration must have the same hardware configuration. They must be the same model, have the same number and types of interfaces, and the same amount of RAM.
Note: The two units do not need to have the same size Flash memory. If you use units with different Flash memory sizes in your failover configuration, make sure the unit with the smaller Flash memory has enough space to accommodate the software image files and the configuration files. If it does not, configuration synchronization from the unit with the larger Flash memory to the unit with the smaller Flash memory fails.
http://www.cisco.com/en/US/products/hw/vpndevc/ps2030/products_configuration_example09186a00807dac5f.shtml#req
HTH
