Since you havn't started yet, you might like to have a look at this Shipbucket page that has a schematic of how the real horizontal Sealslug magazine and a proposed vertical one worked:
http://www.shipbucket.com/images.php?dir=Parts Sheets/Royal Navy Weapons Parts.png
The vertical magazine woulf be particulary suitable for a converted big gun warship, since the magazine could fit in place of X turret and the launcher in place of Y turret.
The Sea Cat director mentinoed by Cliffy B, derived from the MRS3, was actually the third Sea Cat director, known as GWS-22. Here are all the variants (all used the same missile and launcher):
GWS-20 : Based on the STD (Simple Tachymetric Director) and entirely visual in operation. The operator tracked the target via binoculars and steered the missile via radio commands and a small joystick.
GWS-21 : Based on the CRBF (Close Range Blind Fire) director used for 40mm bofors guns. It looked like an open-topped drum with a hemispherical canvas weather cover. In operation, it held two men, one of whom kept the director facing toward the target, and the other who steered the missile. Some versions had a Type 262 radar which could track the target and missile, but steering commands still had to be generated manually.
GWS-22 : Based on the MRS-3 gun director, this was still a manned director, but had radar, TV and visual tracking modes, and most importantly, SACLOS command guidance, i.e. the operator only had to track the target whilst the system automatically tracked the missile and generated command signals for it.
GWS-24: Based on the Selenia Orion RTN-10X radar tracker. This unmanned director consisted of a radar tracker with a TV tracker looking through a hole in the dish. Same MO and options as GWS-22, but contralloed from the Ops Room, not on the mount. This wa the most advanced Seacat director in RN service.
Seacat was very flexible and could work with a wide variety of other fire control systems too. In particular, the Dutch developed a range of systems to control them, based on M-44 fire control radars and the ubiquitous SIGNAAL WM-series "egg" track-while-scan radars.
The Airfix 1/600th County is pretty easy to come by over here, usually boxed as HMS Derbyshire, so if you're stuck, give me a shout and I'll get you one. It was also included in a Falklands boxed set with a Leander and an Amazon: obviously you pay more money for that, but it's an excellent bits mine for RN projects.