IMC1,
Put this little online weight & balance spreadsheet together for the arrow III; 270litres full; 190 litres @ tabs... hope that helps. (Appreciate it's not the turbo variant but the tanks are the same)
http://www.navex.aero/w&bcalc.htm
Great a/c the Turbo Arrow... here's a cockpit snippet of the baby I fly in Zurich...
http://www.navex.aero/ArrowTurbo3.htm
Take care,
EG
P.S. Obviously, the POH will have the figures in USG not litres. If I'm not mistaken I think 2USG is "unusable" off the top of my head.