I came across an interesting website that covers many aspects of Spark and Glow engine history and technical information.

It originates from a chap in BC, and has contributions of information, from all over the world.

Often he has links to little known websites with interest specific information.

https://www.adriansmodelaeroengines.com/catalog/main.php?cat_id=0

If you are a collector of model engines then you might have interest in this site.

https://www.modelenginecollecting.com/index.html