The brake reservoir on the America is 11mm and the one on the Speedmaster which is the same as the one on the Rocket 3 is 1/2 which is a difference of 2mm.
I will run with the 11mm one and if necessary upgrade to the 1/2 if it is needed. Mert is running the 11mm and says she has no problems with the front brake, time will tell

The upgrade to the 1/2 Speedmaster/R3 second hand runs about £75.00 or $160.00 or you could buy new at a cost of £151.00 + VAT @ 17.5% + Delivery (ouch)