There's been a lot of breaking changes since 2.0.8. I'd strongly advise going for a more incremental approach:
=> 2.1.0-pl => 2.2.0-pl => 2.3.0-pl => 2.4.0-pl => 2.5.0-pl => 2.6.0-pl => 2.6.5-pl
Basically, you're upgrading to the next minor version with each install. This is a bit tedious, but it's the safest bet.
UpgradeMODX should be able to handle the upgrades for you from 2.3.0-pl, if I'm not mistaken.
A MODx Fanatic