A bigger issue than converting the license would be getting a job! Unless you are a US citizen (or are married or very closely related to one), or have a green card, you have no chance of getting a job of any kind in the states.
I think you should ask yourself a few tough questions. Is borrowing £45k from a bank really the best way to start out? You should spend some time reading the threads on this site. The job opportunities out there for low time pilots are limited to say the least. Have you thought about how you will qualify for a £45k loan with no income? And how will you repay a £45k loan when you have an fATPL but no job?
You have a good number of hours already so how about knuckling down to the atpl exams, getting a job and then putting yourself through the cpl/Meir as you can afford it from your earnings. Then see where you are in two or three years time.