Hunting an 'Antelope'

[vtsteam]

HH Groves and other early steam powered airplane engine builders used tubes to a central disk valve on opposed twins and radials.

[Sanjay F]

I found this, is this what you mean?

[Jasonb]

It is more understandable on the layouts of aero engines as they were often single acting so needed the steam at the head end of the cylinder and opposed & radial engines had the heads a long way a part so cast in passages would not have been practical. This is not really the case with this engine.

Here is another example with the steam going to the heads

https://myersengineworks.com/product/steam-aviation-engine-casting-kit/

[vtsteam]

I found this, is this what you mean?

Yup.