Some ships they did a forward and after magazine, the ones with the middle turrets (Iso or Kongo, I forget which) don't seem to have one under the two midships turrets. Yamato is just a little behind the second forward turret or the forward edge of the after turret. Be nice if we had drawings showing the exact location of the main magazines for each ship type but I guess our spies weren't ambitious enough.
As for date, in a career (in stock game) there's always some capitol ships at Kobe for each patrol that I've tried it. Sometimes 3 carriers and 2 BBs, once I saw only 1 CV and no BBs but that's rare.
Math, I suck at that too, I decided in 1968 that women and algebra were too complicated for me to ever understand. US Navy electronics school was easy except for the math, I had to take extra classes to learn enough trig to pass those tests, then promptly forgot it all after I graduated. What I use for manual targeting is another cheat - select the mast height slider in the rangefinder, set it to max, hit the - key to set the periscope straight ahead, then send range and bearing to TDC for a zero gyro angle shot. After that I eyeball it in a sort of "angle off" method, set the crosshairs between 10 and 15 degrees (depending on estimated speed) left/right of zero and fire when the target is in the crosshair. With that method range doesn't matter, if it's 500 yards or 2000 yards the angle is the same. Obviously it requires a lot more fish than the stationary targets.