Pushrod tubes of this type are fairly easy to make . The one on the right is original Norton. The left one is fabricated from a length of alloy tube belled with a ball pein hammer. the top part is made on a small lathe.
When the small end of a conrod decides to break it can release hell !
Fortunately valves are still available but I find prices can vary .
On the Norton single both valves are the same which helps as the exhaust usually goes first.
Note I do not have a high comp piston. I follow the dictum of that master P.E Irving.
In his bible " Tuning for Speed" he states..." and it must always be remembered that it is not the actual measured compression ratio which counts, but the pressure of the gas at the end of the compression stroke".
This simple fact is something many people forget.