This is how my HD Aluminium Pushrods looks inside!
The dimension is Ø10mm / Ø6mm length depending on the operational. The material is a special Aluminium with heat treatment and can provide Rm 470N/mm².
This material you can`t get around the corner in the warehouse belive my.
You can handle a valve spring pressure up to 140kg, and thats more then enough for the aircooled Typ1 engine.
I use this pushrods in high performance street engines and in all out race engines.