Believed to be the Columbus Somerset De Luxe. This is a 6-valve + magic eye dual-wave radio, and it is believed to be the big brother of the 705 Somerset. This is all based on advertising pictures and descriptions - actual pictures of a 708 would help clarifiy this.
Intermediate Frequency: 455kc/s
General Construction Notes for Radio Corporation of New Zealand Ltd: The first digit of the serial number typically indicates the year of manufacture of RCNZ chassis' (although not the decade - that requires a little knowledge of the valves, construction, etc). Sets from around 1934 onwards were often (but not always) constructed in a distinctive pressed 'baking pan' style chassis, seemingly unique to RCNZ.