Addendum:

> According to Lauterbach, the APM83290 has a PPC450 core

In contrast to Lauterbach, a new edition of Wikipedia's PPC4xx article claims that Titan was designed "using the PowerPC 440 core spec".

http://en.wikipedia.org/wiki/PowerPC_400#Titan

Either way, there's still something else mysterious about it: According to Wikipedia, PPC440 and PPC460 (and thus I conclude PPC450 as well) comply to Power ISA v2.03+, whereas Titan complies to Power ISA v2.04+ (i.e. not to v2.03). Strange.