I agree Tarawa would be a good subject for Pacific Marines -- most of the gear used there was used in later Pacific battles (LVT-2, M4A2 Sherman, 75mm pack howitzer) and the uniforms there (mizture of HBT utilities and camouflage suit) would serve for all subsequent Pacific battles. It was at Tarawa that the camouflage helmet cover that was worn through Korea first became universal for Marines. Tarawa Marines would work for The Marshals, Marianas, Palaus, Okinawa or Summer 1950 in Korea (by summer 51 the leggings had been discarded). Actually most of the existing Iwo Jima Marines would be useful for Tarawa (the LVT-2 and Flamethrower excepted since the earlier model flamethrower was used at Tarawa, and the LVT's at Tarawa were Gray, not camouflage painted) (The Iwo Japanese figures don't work for Tarawa since they portray IJA and the Tarawa defenders were IJN Special Naval Landing Force/Base Force (Japanese Marines).
Guadalcanal Marines reeally only work for Guadalcanal. The combination of no helmet covers, M1903 Springfields, Reisoing Guns is pretty much unique to the early Solomons campaign.
As I noted above, for Iwo, some figures should be wearing the M41 jacket over their green HBT utilities. Check out theis photo of both sets of Iwo Jima Flag Raisers:
http://graphics8.nytimes.com/images/blogs/morris/posts/11morris12.jpg
(also taken by Joe Rosenthal) and you will see almost all of them wearing the jacket (recognizable by the diagonal handwarmer pockets on the sides). Interestig Joe Rosenthal himself was wearing a later M43 field jacket on Iwo.