That would probably be "AR" (not "AK"). The font seems to be the same Alfa Romeo that used on most other cars of the period. Maybe the top of the "R" is missing or too faint so it looks like a "K"?
[SIZE="1"]'63 2600 Touring Spider (AR 191437, the car that started the 2000/2600 International Register, reassembly in progress)
ex-'65 2600 SZ (AR 856043, the car in my avatar, sold as resto project to Austria)
Maintainer of a private 2600 SZ register (not the one in the Netherlands).[/SIZE]