Very nice open-access details. Your open forward fuselage bay, according to my "Warbirds of the Sea" (p. 260), contains the lube- and hydraulic oil tanks (plus their own armor, forward!), with your upgrade detail looking like a brace of hydraulic lines, going to that tank. The MGs bay is also very cool. I can see some brass-color in there, but can't make out any individual cartridges - did you do anything special for them?
Also, I really like the finish of that dark blue - is that "stinky Testors", or what is it?
Excellent HellCat, Don!