Well the avast release history shows avast 8.0.1497 was released on 2013-09-02 and also indicates there were some fixes related to Win8 & Win8.1, what they were as an avast user I don’t know.

Whether that was for the early win8.1 preview I wouldn’t know, the only thing for certain is that there is no support now for old versions of avast including avast 8.0.1497 as far as program update/fixes are concerned.

If you find that there are any compatibility issues, your only course of action would be to update to a later version of avast (https://www.avast.com/en-gb/release-history) 2014.9.0.2006 reports fully compatible with Win8.1. However, you would have to find an old version of that as that too is no longer supported. Other than that you are looking at updating to the latest avast 2015 10.2.2218 version.