It's an inline 6 cylinder.
One Push Rod controlled the Air Starter System I believe.
Not sure what you mean by Triangular?
Today We use Glow plugs to pre-heat the cylinders.
At first they were run over by air to get the heat to fire by the compression itself.
One Company I do work for has an old engine that has the Air Starter System.
That comtraption is bigger then my house!
I'd love to hear it start up.
But it's been laying in pieces for over 40 years.