Sorry Cyclops: I am afraid I agree with Bill, Typical warbirds have small rudders, wide engine spacing, and VERY heavy wing loading. All this would not be good to learn on with an engine out.
Let me ask Wingspam, do you always fly coordinated with the rudder...all the time...come on be honest. If not, learn on the above planes before spending the $$$ on an expensive war bird.. Then go for it. I have one the above list the most experience with the Cedar Hobbies twin stick. Not only a twin, but a blast to fly aggressively. Good single engine out. Note, loops on one engine require a LOT of rudder and speed!!
Other than that, many less expensive planes lend themselves to conversion, such as most trainers or single engine sticks. I would lenghten the wing span to reduce wing loading due to the extra weight of the engines.
As Bill would say..welcome to Twinsanity.
Twinman