cfa10yrplan

To answer the first question, the real FX rate is based on the nominal FX rate and the price levels in both countries. Not sure if the real GDP amounts for each country can be substituted for the price levels.
In the formula below I use direct quotations. So your example of “GBP per one USD” would be USD:GBP meaning that it’s from the perspective of a UK investor.
FX(real) = FX(nominal) x (price level foreign country / price level domestic country)
So say that USD:GBP = 0.60 pounds and that the price level in the UK was 100 and in the US it was 200, then we calculate FX real as
FX(real) = 0.60 x (200/100) = 1.2 pounds