It sounds good to me.
Only problem I could think of with physics and tree biology would be if you tied the spanline to a leader with a bad inclusion. I reckon the side loading would probably tear it out if you were unlucky. Otherwise treat them both like any other normal TIP.
Just thought of something. Your pulley that your life line will be going through, will you be sliding accross the line while it's taut or will you be using the spanline as a V?
Here are some diagrams to help explain my questions:
Only problem I see with this is that bloody pulley is gunna slide everywhere when you want a nice static position whilst cutting...
Seems good for work positioning only problem is if you don't have attentive groundies... You gotta wait around for them to help you move...
Good luck mate and take LOTS of pics, will be very interesting to see.
P.S What part of Sydney you working in?