Fan replacement from older machines?

Unfortunately, that won't work. The Late 2008 is the first of the 15" Unibody MacBook Pros; the earlier generation used entirely different components. Regardez:

Early 2008 15" MacBook Pro (A1260, MacBookPro4,1)

• Left fan - Apple Part #: 922-7916, 922-8042
• Right fan - Apple Part #: 607-2187, 922-7917, 922-8043, 933-8359

Late 2008 15" Unibody MacBook Pro (A1286, MacBookPro5,1)

• Left fan - Apple Part #: 661-4952, 922-8703
• Right fan - Apple Part #: 661-4951, 922-8702

As you can see, there's no overlap in the part numbers; if you look at the fans themselves, they don't even look alike.

That said, within each group (Unibody and non-Unibody), you can pretty much swap fans around between laptops of the same size, regardless of the generations. The Mid-2009 Unibody 2.53GHz is an odd man out; it uses only a single fan, like the MBP 13" models. But all the other Unibody 15" models use the same fans, so you can salvage them out of whatever machine you can find.

Before replacement, you might want to try opening up the machine and cleaning whatever gunk the fans have collected over the last seven years (there's bound to be a bunch of stuff, especially if it lived in an environment with furry animals around). That alone may resolve the noise problem, without replacing a fan.