The Cyclone III development board you have (DK-START-3C25N) features the same High Speed Mezzanine Card (HSMC) as the DK-DEV-3C120N development kit the SDALTEVK daughter board was originally promoted with.
So, the SDALTEVK daughter board should simply plug onto the HSMC connector, J1. A quick look at the schematics for the two development boards shows the HSMC pinouts are the same.
Refer to the
hsmc specification (
http://www.altera.com/literature/ds/hsmc_spec.pdf) for more details.
What differences are you concerned about?
Cheers,
Alex