I have been involved in advising US and overseas lawyers/graduates in applying for UK based roles so many times and application forms can be very difficult indeed to complete.
The main thing is to make sure that you assimilate to the UK standards, with A levels rather than High School graduation certificates, degree classes instead of GPA points or similar.
Try to put every qualification in UK format first, with your actual US level afterwards. Usually application forms are filtered by someone who has to look through about 200 applications and what they want to see very quickly indeed is:
- a 2.1 degree or higher
- A levels at grades AAA, ABB, AAB etc.. and no evidence of a slip up.
If they cannot see these, unless they consider your work experience to be fantastic, you will find yourself getting rejected a lot of the time. This is even if you are a graduate from Harvard and went to the high school that is in the musical with lots of basketballs…
Assimilate, as the Borg once said (I think), and the world will be your oyster…..