dump from 8.x restore to 7.3.x

Hi to all,

We have a pretty big database that is going for an upgrade (PG7 -> PG8)
in the next few days, we have tested all the features of our application
but we cannot be sure that everything will work out perfectly (db is
managing several blob's only tables that have proven to be pretty hard
to configure).
I am currently investigating a worst-case-scenario strategy that would
be to downgrade the database from PG8 to 7 if anything goes wrong;00
this implies that we:
1) dump from a running PG8
2) remove PG8 and reinstall PG7
3) restore the dump into the running PG7

unfortunately pg_restore complains about the dump header and doesn't
restore the db at all, having tried to dump with both -Ft and -Fc flags

shall I try the "--ignore-version" option in pg_restore?
is there going to be any problem in using this option? (corrupted data,
tables, etc.)

Thanks, any help appreciated
Edoardo