Hi Cory. You are about to set out on a journey I have just completed (almost), and the road, my friend, is rocky and marshy!
I have gathered a fair amount of info on the FAA Avengers, including the differences betwen MkI and II etc. I have a few B&W profiles, and can point you in the direction of some colour ones, but! It would seem that even some of the 'official' sources have some conflicting, and at times confusing, info when it comes to markings, codes, and particularly roundels. So far, regarding the latter, I have discovered possibly 3 different styles of SEAC roundel, and at least 2 different Pacific Fleet roundel, and there appears to have been a mix of these too!
Not all FAA Squadrons carried a fin code as a carrier or group I.D., and this is possibly due to the Squadrons moving about as it were, between land, and DIFFERENT carriers!
If you go to the FAA Archives web-site, which I think you've looked at already for Corsiars, it's a good start point. It's possible to cross-reference between aircraft, Squadrons and ships, and get most of the details required. However, be warned, some of the info is conflicting, and some of the images, pictures and profiles, can be spurious or dubious when it comes to a specific date. It would appear that some Avengers in particular, retained SEAC/East Indies Fleet roundels and other markings after transfer to the Pacific Fleet. As far as code letter decals are concerned, I can possibly help you when you decide which aircraft you want to portray. But again, beware, as some info shows, for example, a particular Avenger as being a MkI when it's a MkII, and vice versa! There are ways to tell in photos, but the only true way is by the serial number, and I can assemble the serial blocks and dates etc for you.
I'll TRY to get something basic together soon, but I'm having bl**dy awful Internet problems at the moment, operating at snail's pace on 2G only, and the mobile 'phone company can't yet identify the fault!
Out of all the FAA Avenger Squadrons, it appears that only 5 or 6 might be in action in one particular area at one time, as their operations 'jumped about' for want of a better description, due to the vast distances travelled during the course of the period from mid 1944 to early 1945. For example, using just one Squadron as an illustration; pre D-Day operations in the English Channel, D-Day support operations. Move to the Med, support further aliied landings. Move to the Indian Ocean, across the Ocean. Attacks in support of US operations, more moves. Into the Pacific. Attacks on Japanese oil and transport infrastructure. Move further, first attacks on Japanese Islands, attacks on Japanese 'mainland'. All in the course of 14 months!
This is only what I have gleaned so far, without any previous knowledge of the FAA, let alone Far Eastern ops, and without what I would consider in-depth research.
Anyway, I'll post what I've got as soon as I can, and you can take it from there, and let me know which way you want to go. If my bl**dy Internet keeps going!
EDIT:- I forgot to mention. Even though the Italeri kit includes markings for a FAA Tarpon/Avenger I, this can not be modelled OOB. It would need some modification to the engine cowling and forward firing armament, as well as other small conversion work. It's possible, but a bit involved. So, unless you want to do this work, you're restricted to the Avenger II.