Valve identification
 

I have 6 Porsche valves that were sent to me about 15 years ago when I was rebuilding my 1969 911E. I remember that they were not for my engine, but never got around to sending them back. They are marked TRW 3072.

They are approximately 108.5 mm long, 9 mm dia stem, 41.5 mm dia head.

Does anyone know which engine they are for?

Build your own boat so you can grow and become an expert of it. Try to learn from the experts and apply it to your own boat. Learn from others' and your mistakes. From there, develop your own techniques so you can do it your own way. Modifications are of course for the better. Try to improve the time required in doing some parts, or try to improve mechanisms for improved quality. You can use alternative materials to improve durability of your boat too.