"(Mushashi took 17 torpedos and 20 15,000 pound bombs. For comparison, the strongest bomb that the US had, short of the Nuke, was a 5,000 pound bunker buster IIRC. That is an incredible amount of firepower no matter how you slice it.)"
How could the Americans drop 20 15,000 pound bombs if they only had 5000 pounders?
"Yamato-classes armanant was nine 18.1 in. gun batteries, which wa sdivided into the same 3 gun battry arrangement as the Iowa-class. Her secondary armanant was 6.1 gun batteries, and had a smattering of 25 and 13mm gun batteries, which like the Iowa's 40 and 20mm were used for anti-aircraft duty."
Japanese ships didn't have a 'smattering' of AA guns:
Iowa:
9 x 16 in (406 mm) 50 cal. Mark 7 guns
20 x 5 in (127 mm) 38 cal. Mark 12 guns
80 x 40 mm 56 cal. anti-aircraft guns
49 x 20 mm 70 cal. anti-aircraft guns
Total: 149 AA and Dual Purpose (anti-air and anti-ship) guns
Yamato
9 x 46 cm (18.1 inch) (3 × 3)
12 × 15.5 cm (6.1 inch) (4 × 3)
12 × 12.7 cm (6 × 2)
24 × 25 mm AA (8 × 3)
4 × 13 mm AA (2 × 2)
Total: 40 AA and DP guns.
(In the FS universe, I'd compare the Yamato to an FS2 era Orion, and the Iowa to a Hecate with BGreens on the sides instead of the TerSlashes.)
Back to the Iowa vs Yamato topic, and reality:
If I was captain of the Iowa, I'd give the Yamato a
night it would never forget- from sunset to sunrise a shower of 16 in shells from beyond the horizon. And I'd be untouchable- no radar for the Japs = no aiming at me.
If I was in charge of the Yamato, I'd have to attack during the day to see my enemy, and I'd need some luck to
damage the Iowa without getting shot up myself, and even more luck to do it fast enough to fall back before the US Navy sends 500 airplanes to get me.
Summing up- I think the Iowa would either win untouched the night before the battle, or win with the help of a local aircraft carrier if SHTF.