How can I jettison Safari 5.1.10 and return to 5.1.7?

5.1.10 is driving me crazy! It crashes constantly, & the Web Kit reboots regularly, generally when I'm right in the middle of writing something lengthy. It eats up RAM & CPU Usage, often won't play videos, and the autofill is useless. I think I can revert back to a better working version by perhaps downloading & reinstalling the combo file of 10.6.8, but am not sure how exactly to do that.