DDK - Die Deutschen Klassiker

Hi, I currently have problems with the dipstick on my 916-6 conversion., it doesn't read anything despite the tank and engine having been filled with the correct amount of oil. From what I can tell from investigating, I may have the wrong parts, I believe both the dipstick and the filler tube are from a 911. The dipstick is definitely too short. However, the filler tube I believe is also too long. Can anyone tell me the difference in length between the 911 tube and the 914-6 tube? It appears the original 914-6 item also fits into the tank neck making it shorter. The 911 filler tube just butts up to the tank filler tube.
I would be grateful if someone could help me with the correct dimensions. I believe the correct length 914-6 dipstick is available in the USA, or I could alternatively modify the one I have. Cheers Jonathan