Yeah I think Ray is probably under-selling his weight. Perhaps that's the joke? If Ray is 15, he hasn't gotten his adult muscle weight yet, but he is probably pushing 260 let alone 160. He's larger than Fatty and Algie right, or are they the same? I know he looks fatter to me.
Heights are strange. If Jimmy is around 5'5", then I think the average sized boys (like Trent or Ethan) are probably 5'9" or 5'10". Damon and Bif are around 6'2" or so. I think Russell is 6'5" or 6'6" and probably upwards of 350 pounds. Dr. Watts is pretty damn tall, but I don't see him around alot. I don't think Hal is anywhere near 300 pounds.