Pretty much all model engine fuel contains some Nitromethane - I presume that is why you refer to these engines as nitro engines:
As such, the question becomes, are you looking for 2 stroke or 4 stroke model engine plans?
How about this? http://www.metalstop.com/engine/plans/plans.shtml
Yielding this: http://www.metalstop.com/engine/videos/beco2.mpg
4 stroke: 4 stroke model engine plans - Google Search=
for instance: Glen's Machine Shop: The latest progress
2 stroke: 2 stroke model engine plans - Google Search
for instance: Projects In Metal, LLC » Blog Archive » Free Metalworking Project Plans: A Simple Two Stroke IC Engine