Thanks for the feedback, guys.
I've spent the last two days trying to build his body - the first seemed too small and not rounded enough, the second is too large. I've learned the hard way that once a foam body is skinned in antron it significantly changes the perception of its size...add to that the fact that a very slight change to the curves cut in flat foam (we're talking mere fractions of an inch) can result in quite major difference to the assembled structure, and this body patterning is turning out to be more challenging than the head! Especially when you realise that his body is't just a sphere or a tube, but slightly teardrop shaped, with a flatter curve to the front/chest than there is on the back/butt, and the shape itself looks very different when we see a picture of Kermit sitting in a chair with legs visible, vs when he is essentially cropped from waist up, etc etc etc.
My initial plan was to use the fabric patterns revealed from the disassembled Master Replicas puppet (which conveniently could be scaled appropriate to the measurements I'd used for my head) to dictate the size of the torso and almost reverse engineer the foam understructure, but for the life of me I cannot work out how the front pattern piece would be attached to the two pieces forming the back.
So I've been taking the approach of using two, 3-petal pieces of foam and then just draping the antron rather than going from a fabric pattern...as I said, though, that hasn't been too successful.
Any builders of Frogs out there have any advice about the body dimensions? If you're able to tell me anything about the length of the body in proportion to his mouth plate, etc. Or is there anyone who can work out how the 3 torso pattern pieces should be assembled?!