Pardon my landlubber's ignorance, but what was the rationale behind the armament distribution in Japanese heavy cruisers? The Tone Class is all guns forward, all the others have one turret with a restricted arc of fire, Furutaka looks like it lost a turret...

From Nihon Kaigun

See here for images: Japanese Heavy Cruisers

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I'm not an expert by any means but...

I think the Tone class were built (or was that rebuilt) as scout cruisers and their back ends were used for sea plane launching and hangers.

The others are from the "turret farm" school of ship building. If you put more than 4 turrets on a ship some will have restircted arcs unless they are light enough to go three levels high (like the Atlantas). Note that some of the older US BBs and the Brooklyn class CLs had similar limitations on some of their turrets.

I agree with lwd, a turret farm is a good explanation.
One of my youthfully favorite ships was HMS Agincourt. Probably still the "King" of throwing shells in one direction. 7 twin turrets of 14 in? all capable of firing broadside...at once.
It was said she'd roll over if she fired a broadside, but this was proved wrong at Jutland where she fired 10-12 broadsides. The rest of the "Grand Fleet" thought she exploded (blew up) every time she did. It must have been quite a show!
The Tone & Mogami classes were both originally designed as Light Cruisers with triple 6.1 (DP) inch guns. Same amount and placement of turrets. To get more boats for the weight/gun, requirements/limitations of current treaties.
Once started (known/observed)(they do take a while to complete), they could be, and were, easily converted to overweight, overarmed (per treaties) Heavy Cruisers. A clear violation, as were many ships in most Navies (especially the IJN).
The Tone/Chikuma were touted as the eyes/ears of the fleet for being able to operate so many float planes. Up to 6, I believe.
There was a problem with having heavy guns firing near float planes/hangers/catapults with collateral damage to the planes from concussion, fire, etc..
Perhaps why Americans chose that middle hull position?
Even Battleship So-Dak had set a serious fire to one of her planes, during a manuvering battle at Guadalcanal. Turned out to be no problem as another salvo blew the flaming plane overboard.
Chikuma/Tone solved that problem by having the main batteries forward. The arrangement is probably to save weight. A Barbette (a tall one), is as heavy as a turret (almost), so keeping them flat as possible, and still having them available in a broadside, will by reducing weight, add speed, and fulfill the semi-original design/purpose of having a fast, seaplane loaded, capably armed CL to CA "Hybrid" scouting Cruiser.

I'll wait for Mr. Gardners corrections

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The main reason that the Tone class went to the extreme of having all turrets forward has primarily to do with Japanese naval doctrine when they were designed and constructed. Doctrinally, the heavy cruisers were the primary scouting force for the fleet. Their float planes were by doctrine performing the equivalent of US carrier scout bombers (SBDs in another role).
The most famous example of this the scout that found Yorktown at Midway but had radio problems.
Anyway, the Japanese thinking was that by using float planes from cruisers they were not risking their carriers and were not interfering with flight operations from them or reducing strike size by having to launch scout aircraft.
The US got around the flight operations problem by building a awarthships catapult into the forward end of their early carrier hanger bays. This was supposed to allow launch of a scout bomber without interfering with the deck park or strike aircraft.
US heavy cruisers carried float aircraft for primarily gunfire control / spotting and as liasion aircraft not as scouts.
In the case of Tone leaving the rear of the ship clear of guns, etc., made recovery using either the ship's crane or Hein mats easier than trying to do this with the amidships arrangements on earlier classes. The Japanese were obviously willing to suffer the penalities of limited arcs of fire for their main battery in order to improve scouting operations on these ships.

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