Postgresql and Oracle

Not an advocacy post. If I want advocacy, I know where to find it.

I have an application that uses Postgresql - nothing too fancy, some
plpgsql, a couple of custom types, lots of text and no varchar.

For business reasons I need to also support Oracle. On the app side
this is not a big problem - I'm already using a DB-independent access
library (Qt) and most of my queries are fairly vanilla SQL.

On the database side it's a little more complex. I'm looking for
resources comparing the two, and advice on porting PG -> Oracle
(though I suspect that any docs about Oracle -> PG porting experience
might be useful too). Google finds a bazillion advocacy comparisons,
which makes it hard to find anything more useful.

I already know about OpenACS (a fairly database complex CMS written
for Oracle and ported to Pg) and their docs. If anyone has any other
pointers, they'd be appreciated.

(If it's relevant I'm currently on 7.4, but would be looking at
comparing 8.1 and 10g).

Cheers,
Steve