How to grind a 1.3 starter to fit 1.6:
Step 1: Grind

Step 2: Grind some more

Step 3: Better grind it one more time

Step 4: Admire grinding skills

Step 5: Smooth it out a bit

Step 6: Rust protection

To fit:
Disconnect battery, Remove airbox, remove original starter, put new starter in, re-fit airbox, re-connect battery...