Most of the small Davies Charlton engines shared a similar appearance, but the cylinder heads were anodised in different colours. That only applies to the air-coxed versions, though!
I used DC Dart, Merln and Spitfire engines in control line models back in the early 70s, there was also a 1.5cc engine in the same series but I can't remember it's name. They and some bigger engines (DC Rapier, 3.5cc from memory) but I never actually saw one in use.