AMT did the Allison in 1/25.
In 1/24, Airfix and Trumpeter have done a number of WWII aircraft (Mustang, Spitfire, Hurricane, BF 109) which would have R-R Merlins, Daimer-Benz, and so forth. These kits can be expensive but you might ask around and find an aircraft modeler building one "buttoned up" and therefore not really needing the engine.



