What is the best mpg i can't expect from a 1997 jetta td AAZ

[IainS]

My last check in my 1997 1.9 TD was 6.85 L/100 KM or 41.24 Miles per Imperial Gallon or 34.34 Miles per US Gallon.  The only thing I can really suggest for improvement is a 5th gear swap or a ring and pinion swap to get the rpm range down into a more fuel efficient range. (or find a good TDI donor)