It was called a bunch of things, Weapon System Alpha being the most common.
No conversion for Weapon System Alpha exists that I'm aware of, but it's simple enough to scratchbuild... Here's some history behind the unit...
It's official designation was the Mk 108 launcher, which fired the Mk1 and Mk2 12.75in. underwater rockets. It was completely remote controlled, and auto-loading.
The mount itself consisted of the rocket launcher guide, carriage, stand, shield, and power drive unit. The guide was a 12.75in. tube open at the breech and muzzle and pivoted on the trunnion bearings of the pedastal. The guide could be depressed to 10 degrees, and elevated to a loading angle of 90 degrees. A cone-shaped blast deflector was attached to the muzzle to deflect the rocket blast back away from the rocket as it was being launched. The pedastal was mounted on a base ring type carriage that supported the rotating assembly in the stand.
The mount was provided with a circular shield for protection against weather and rocket blast that was not re-directed yb the muzzle shield. This shield also collected and vented the gases from the muzzle shield directly upward over the top of the unit.
Everything else about the unit takes place below the actual launcher, the ready storage lockers for the unit, power drive units, etc., are located below the deck level of the unit.
It you're converting the Tamiya Fletcher into the postwar Eaton, you'll need to add the tripod masts, fore and main, convert the bridge structure considerably, replace the 40mm with 3"/50cal AA with MK 19 Mod 1 radar, MK 63 Fire Control radar on a Mk 14 Director radar, and SPS-6 or SPS-10 air search radar. You'll also need to lose the torpedo tubes and replace them with Mk 32 triple mounts. There's a chance she carried the Mk4 launcher...you'd have to research that further.
It's a major undertaking, basically, the only things you'll retain are the 5in guns, funnels, and deckhouses. Everything else, bridge, masts, torpedo tubes, AA guns, will all have to be replaced.
Good luck, would love to see it when it's done!
Jeff