There are other motors that Revell issued originally which are now extremely rare, among them a Buick Nailhead, a 392 Chrysler Hemi and an injected '63 Corvette V8.
FWIW, the 392 Hemi is rebopped in the Revell Miss Deal kit. It's identical as far as I can tell, except for the different exhaust headers, and the point that all the pieces are chromed in the Parts Pack version, vs. only those you'd actually want chromed in the Miss Deal kit.
I agree that the 327 Chevy Parts Pack is the hardest to find.
Also, I haven't read the entire thread so apologies in advance if I'm repeating something already said but many of Revell's full model kits of the early 60's contained engines that were designed in the same manner as their Parts Pack engines. I'm particularly fond of the Cadillac in the Outlaw kit (which is similar to the Parts Pack Cad but has different building options including the intake manifold/carb setup), the blown Olds in the Beatnik Bandit (some really cool parts on that one), and even the 409 Chevy optional engine in the original Revell '55 Chevy kit.
In any case, like others have said here, these Revell Parts Packs are cool engines, with excellent period-correct speed accessories, that are generally a fun and authentic build.