AFRA replica heads have been criticised for the quality of the castings, but I know that
SAS Engineering in the UK made a batch of 10 GTA heads a couple of years ago for John Shipman, and the quality looked superb. I'm unsure of the specific differences between 1300 and 1600 heads but I imagine the ports to be smaller. Perhaps the heads were supplied unmachined to be finished as required. Maybe you could contact John via SAS and see if he has any left? You should also contact Richard Banks at Alfaholics, as he's now concentrating on sourcing original parts for these cars.
Good luck ...
Alex.