Can try Below:
1. Frequency = 100K
2. Np=25T, Ns=3T
3. air gap=0.17mm Lp=362uH
At Vin=65Vdc
Ip=1.5A
Bac=130mT, Bdc= 148mT Total B=278mT <300mT
Duty=39.1%
MosFet voltage =107V need to check the peak voltage caused by leakage inductance.
reverse voltage on output diode of 5V = 12.8V, can use 45V schottky.
4. Core I used for calculation is EE25/13/11 Ae=78.4, le=57.5mm