Your thinking is correct except you have to assume that:
1- the engine is in time and has not perhaps slip a tooth prior to replacing the timing belt.
2- what happens if you remove the old and a cam sprocket moves, what point of reference do you have to put it back into position?
Lining the marks up at TDC will give you a absolute point of reference.
- This reply was modified 1 week, 3 days ago by Richard Kirshy.