Indexation was abolished in 2002, so you only get indexation for the years before that. If you inherited the house in the 96/97 tax year, the indexation factor is 1.251 (so you are treated as if the house cost €62,550). If you inherited the house in 97/98 the indexation factor is 1.232.
Using the 1.251 indexation rate, your gain will be €437,450 and your tax would be 20% of this which is €87,490.
If this house has been your principal private residence at any stage during your ownership, the tax will be reduced (or possible eliminated in full).