Engine Numbers?

[Oka]

Just found an answer here:
http://www.volvoxc.com/forums/showthread.php?11752-Engine-Serial-Number

I went to check mine and found out it needed cleaning to see the numbers better (Alaskan engines gets very dirty).
The cleaning solution cleaned off the prints clean and I am left with just white label. The other location is too hidden to see from the outside.
How else can I find my engine number. Can I just get the part with the year and model of the car (that should be enough). Right?

How are the engine number ranges set? The parts stores refer to engine number in ranges.
Eng. No. 3188689 & After or Eng. No. 1266128 & After

Thanks.

[JRL]

What year, what part?

[Oka]

Timing Component Kit With Water Pump for 2001 XC70.

There are Engine No. 1266127 & Before, Engine No. 1266128 & After and Engine No. 3188689 & After.