One of the slickest engines for warbirds this size --is the ZDZ40 RE (rear exhaust ) the entire engine will fit in a 3" wide cowl
HOWEVER
Warbird guys--- unless they have a background in performance flying, are notoriously bad about figuring out airflow and the idea of a can or a pipe - seem sacrilege.
here is shot of one of these with a muffler can - which does not limit power and sounds great and is not a tuned device - with this setup a 21x8 Mejzlic prop puts out excellent power - around 7000 rpm (as an example
So depending or your preferences - opt for a good industrial modified engine ( more cooling fins but a side carb and a siade exhaust ) or for full enclosed setup get the 40 but you must do a good cooling flow setup internally or you will cook it .