If I had to choose, these would be my choices. I know that some of them are A&A OOB units, but I consider the FMG units to be replacements for the OOB units (for the most part anyway) and I would thus like some better quality iconic units:
CV - Shokaku Class
BB - I’m torn on this one; Yamato class were the iconic class of IJN BB, and would represent new BB production. However, the Kongo class would represent the backbone of the IJN BB surface fleet; they saw far more action than other Japanese BB’s in 1942 (due to their greater speed). I’ll leave it up to FMG to decide what mold to choose, and I won’t complain about what I get… (Too bad FMG isn’t producing two BB molds per nation - each nation in the game would benefit from having a pre-war and modern BB mold, IMO).
CA - Mogami Class
DD - Kagero Class
SS - B1 Class
AK/AP - Standard Merchant - I forget the exact designation of the variant of which I’m thinking, as several variants of standard wartime production merchant and auxiliary vessels were produced under direction of the Japanese government during the war. The variant of which I am thinking was approximately 5,000 GRT, and had an aft-engine forward-cargo hold configuration; it was the same variant included in the original Silent Hunter game, although the displacement and dimensions from Silent Hunter were completely inaccurate. I’ll post a screenshot of the silhouette of the Silent Hunter Standard Merchant (taken from Hawke’s Silent Hunter ID Manual) at the end of this post, and try to come up with a better picture later.
Fighter - A6M2 Zero “Zeke”
Fighter-Bomber/Tactical Bomber - B5N2 "Kate - At this scale, the mold could also probable be the Kate’s late war replacement, the B6N2 “Jill” - slightly different tail and cowling, other minor differences.
Bomber - Ki-67 “Peggy”
Heavy Bomber (If produced by FMG) - G8N “Rita” or G5N “Liz”
Air Transport - L2D “Tabby” (US DC-3 Mold can be used here with 100% historical accuracy)
Tank 1 - Type 95 Ha-Go
Tank 2 - Type 97 Chi-Ha (unless FMG is aiming for a medium and heavy tank for each nation; then use the Type 97 and either the Type 3 Chi-Nu or one of several never-completed Japanese heavy tank prototypes).
Half Track/Mech Infantry - Type 1 Ho-Ha
Artillery - Type 90
Truck - I understand these will be generic, so I shall not list a choice here.
EDIT - Standard Merchant Profile from Silent Hunter: