Hangar 9 has updated their '.40 size trainer' Mustang: now you can add retracts:
http://www.horizonhobby.com/Products...ProdID=HAN4440

Also available in RTF version with 2.4 GHz system:
http://www.horizonhobby.com/Products...ProdID=HAN4425

Even before the update, I considered that to be THE BEST warbird trainer.

But if you really think there are too many Mustangs at the field already (as I do): a good P-47 is great choice. I have the Top Flite version, and it flies and handle much better than my Top Flite Mustang, but I'm thinking the Hangar 9 P-47 would be an even better choice (lighter, even easier to fly):
http://www.horizonhobby.com/Products...ProdID=HAN2975

OR, there is an ever increasing number of electric powered 'foamy warbirds' available, which are very good looking, yet easy and inexpensive to.

There, I've contributed to the monthly (sometimes bi-weekely) 'what is best warbird trainer' thread.