Personally, as being a self proclaimed 51 pilot, I'd rather just see the just the RAF Mustang I (2 .50s and 4 .30) with an Allison powerplant, the Mustang II  (Allison powerplant w/ improved supercharger).  
Specifications
Model  -  Mustang I 
Production  -  620 
Length  -  32.25 
Height  -  12.2 
Wingspan  -  37.04 
Weight - empty  -  6536 
Weight - normal T.O.  -  8600 
Weight - max G.W.  -  10,600 
Powerplant  -  Allison V-1710-39 
Horsepower  -  1,150 
Propeller  -  Curtiss 3-bladed electric 10'6"  
Max Speed  -  388 @ 15k 
Service Ceiling  -  30,800 
Fuel Capacity  -  180 
Drop Tanks  -  na 
Range  -  750 
Guns  -  2x .50 cal, 4x .30 cal 
Bomb / Rockets  -  na 
 
Also the standard A-36 Apache would be great, considering the theaters of service it particpated in.
Specifications
Model  -  A-36 
Production  -  500 
Length  -  32.25 
Height  -  12.2 
Wingspan  -  37.04 
Weight - empty  -  6087 
Weight - normal T.O.  -  8600 
Weight - max G.W.  -  10,700 
Powerplant  -  Allison V-1710-87 
Horsepower  -  1325 
Propeller  -  Curtiss 3-bladed electric 10'9"  
Max Speed  -  356 @ 5k 
Service Ceiling  -  25,100 
Fuel Capacity  -  180 
Drop Tanks  -  2x 75 gal 
Range  -  750 / 1375+ 
Guns  -  6x .50 cal 
Bomb / Rockets  -  2x 500 lb bombs 
I've often wondered why the Mustangs didnt have the multiple variants in AH like the 109 series or the Spit Series.  Looking at the generla shape of the planes, I dont think it would be overly hard for the talents of HTC to incorporate.  So bring in more Mustangs, but leave the cannons at home.