Boy you guys got me checking my Cessna to see if it was set up any different then yours and basically mine is the same and I have NO problems getting it off. Here are a couple more things to check.
1. Check that your floats are IN LINE. Measure them front and rear.
2. Double check your CG, mine is also 75 mm.
3. Maybe try a 12/6-3 bladed prop.

In your #4 photo it looks to me like you are not really getting up on the step before letting off a little on the elevator, due too?? not enough power or not enough elevator ???

I fly mine with an OS 91 4c and a 12/6 3 bladed prop. I haven't had much use for 3 bladed props on smaller 2 cyl eng but I love it on the 4 cyl. The 3 bladed gives a little more clearence above the floats. I hope maybe something here will help you as this is one Super float flier. ENJOY!!!! Red