PAK-FA will serve as foundation for FGFA. I am assuming FGFA is the Indian name for PAK-FA?
Like there are several names for F-17 Thunder,
As JF-17, or FC-1 or Super 7.....depending on which country used them.
WELL I PRESUME DIFFERENCES ARE SIGNIFICANT
1. FGFA WILL BE TWIN SEATER
2. ISRAEL AND INDIAN COMPUTERS ON BOARD
3. ADDITIONAL INDIAN A-2-A MISSILES LIKE ASTRA
4. PAK-FA WOULD BE INSTALLED WITH NEWER 17.5 TON THRUST ENGINE MUCH EARLIER THAN THE FGFA
5. PAK-FA WOULD BE LARGER AND HEAVIER THAN FGFA