My guesses are:
1. 3 degrees would add 3 * 0.1 to CL giving a CL of 0.72 instead of 0.42. This is an increase of 0.72 / 0.42 = 1.7 ish.
2. 50 lbs total max force. 6g max LF therefore stickforce gradient is 50/6 = 8.3lbs/g
3. use r = V(squared) / (g x tan (angle of bank)
The important bit to remember is to have the same units i.e. convert knots to m/s i.e. 300 kts = 300 kts x 1852 m / 3600 secs = 154 m/s. This gives the right answer.
I think that's all correct, but it's been a while since I used my brain.
FIS