As they say on eBay, "I'm on expert but" as close as I could get to measuring the trunion, it is 6.5" and "IF" the trunion diameter matches the bore diameter, then this chart from, "British Artillery Ammunition 1780" by Adrian B. Caruana, states:
Nature of iron gun: 32 pdr caliber 6.410 shot 6.105 windage 0.305
Does this help?