Took to thinking about what little we know. One thing Cubicle 7 has told us is that the rulebook is 320 pages long. At the moment I believe that the 320 page total of the core book is a result of taking WFRP second edition rulebook (259 pages) and adding The Old World Bestiary (131 pages). That makes 390 pages, but shave off the fluff section and we’re down to 54 pages of beasts, and then we land at 309 pages.
We can remove 9 pages of beasts from the core rulebook, and that would give about 20 pages extra for fluff if C7 wanted to add some of that to the rulebook. So give or take some info here and there and we are in the vicinity of 320 pages.
We could also be looking at a combination of the second edition rulebook (259 pages), The Old World Bestiary (131 pages) and Sigmar’s Heirs (131 pages). Cut out the beasts (9 pages) and the info on the empire (14 pages) from the rulebook, add in the GM section of OWB and then add a slightly edited SH, you could land close to 320 pages.
The first one (core + OWB) seems the simplest. The second one (core + OWB + SH) is what I would have done.