Jupiter's ionosphere peaks between ~600-2000 km altitude.  The lower peak is better suited for Chapman values, where the temperature would be about 600 K and the neutral density is of order 10^17 m^-3.  Relevant references might be Yelle and Miller (2004; Jupiter book, chapter 9) and Barrow and Matcheva (2011; Icarus).

The situation is similar at Saturn, with ionospheric peaks between ~1000-3000 km.  Typical values near the lower peak might be 300 K for temperature and ~10^11 cm^-3 for neutral density.  A good reference for Saturn would be Nagy et al (2009; Saturn After Cassini-Huygens book).

Altitudes in the giant planets are referenced to the 1 bar pressure level.  Both Jupiter and Saturn can be treated as being dominated by H2 in the neutrals and H3+ in the ions.