Hi KC,
Yes, conceptually this should be still working, but since there were several API changes between Kentico 7 and 8.2, we would strongly recommend to follow the most recent documentation on how to develop custom payment gateway.
For example, there is no need to use WorldPayLoader.cs class file from this webinar code samples anymore, since you can register your payment gateway class directly in its code as explained here:
https://docs.kentico.com/display/K82/Creating+a+custom+payment+gateway
Unlike in my example where I was using GetPaymentDataForm() method to load the payment gateway form control, you can just use GetPaymentDataFormPath() method to load the form control by its path.
Thank you!