Thanks Gnomey for your care!
Those kind words really encourage me.
Attached image shows my measurement on the parts from simply curiosity.
It is approximately 173mm or 6.75inches though I do not know if this value is correct as I have no detailed blueprints of the engine but photos only.
If anyone knows the right answer, will you let me know?
Taking this opportunity, I would like to know how accurate or inaccurate my measuring skill is.
Thanks!