im looking at a used jetcat turbine it is around 140 to 160 size im thinking

it has the race flag around the purple bell end

it has been converted to kero start with 6.0 ecu box

any ideas what to look for or what to measure to determine the exact model size

There was no P140 with V6 ECU. In that can size there was P80, 120, Titan and 160. If it has checkered cowl and has been converted to Kero-Start with external plug, then it is a SE model, a checkered cowl with internal kero-start = SX.