Different calibers, and thus differing bolt faces for their respective cartridges, but the same internal receiver dimensions, bolt rail heights and width, and overall length of carrier travel. There are differences between the AK and Galil or Valmet stock [square fitting as opposed to round] and in the foreend furniture and sights, but nothing overly drastic. The Galil uses an ambidextrous safety/selector lever, since when its stock is folded across the right side of the barrel, access to the Kalishnikov-design lever is limited. But the external dimensions of the rifles' bolts, as they ride in their respective carriers, is the same.
Magazine wells and catch assemblies are a bit different, again, not too severely so.
IIRC, the initial comments made regarding the Galil, when first introduced, made reference to evolved changes to the operating system, inspired by the Stoner designs, in order to enhance lock up and thus accuracy. Galil's use M16 magazines so the geometry has to be slightly different in the lower receiver.
Nope. Galils use a magazine derived from Stoner's M62 Stoner LMG, as used by the US Navy SEALS in it's belt-fed Mark 23 version. The magazine for a .223 Valmet M76 can be made to work in a Galil with a little careful attention to the magazine catch lug. There is an adapter to allow the use of the M16 rifle magazine in the Galil, but most Israeli tank crew prefer the steel Galil magazines, less likely to dent than the aluminum M16 mags, and which hold 35 or 50 rounds in the Galil, rather than the m16 rifle's 30-round capacity.
Now I am curious - since building a licensed Valmet in 556 would be cheaper, why bother developing the Galil?
The sights are arrangesd somewhat differently, but the Israelis wanted a number of features specificly for their theater of operations and to replace the conglomoration of FAL rifles, FALO and FN-Model D BAR automatic rifles, Uzi SMGs and US M1 carbines and AK47s previously in use. And they wanted a full-auto capability more controllable than their FAL rifles had been, particularly by female Israeli troops. And of course, the Israelis had no manufacturing rights for international sales of their previous automatic rifle, the Belgian FAL.
Note too that the Swedes considered the adoption of the FFV-890C Galil variant before deciding on the FNC as their replacement for their older H&K G3s before choosing the FN-C carbine as their *AK5* current-issue rifle instead.
That was a particularly clean Galil variant, and might have become as salable to other Scandanavian nations and their neighbours as the Galil has proven to be: to Guatemala, South Africa and Estonia, among others- and maybe Turkey, if they don't go for the Tavors.