I'll try to explain it... They all say 80cc but that's becasue the way they measure the displacement isn't the same way we measure by bore and stroke alone, when we measure by bore and stroke, the engines are really 66cc if they got the 38mm crank stroke or they're 69.8 or so cc so you'll see people calling these engines 69 or 70cc, but still most of us just call it a 66 because it's less confusing.
Now if you throw in the 13 or so cc's of the combustion chamber into the mix then it'll come up to 80cc, but this isn't the true displacement since the combustion chamber volume doesn't truly effect the ture displacement which is just bore and stroke. There is also another displacement that almost nobody uses called the effective displacement, this is measured from the top of the exhaust port to the top dead center multiplied by the bore, this number is about a third of the true displacement so nobody uses this as a method to advertise their engines.
Pretty much the only way to get a true 80cc's from these engines would be to stroke the crank as much as one could get away with and bore it out as far as they could get away with, then the bore needs to be re plated with nikasil or it wouldn't last very long at all.
You can put a 66/80cc piston and top end on the 60cc and probably even the 49cc to get more displacement, but to get a true 80cc from these engines, you'd either need to go up to about 45mm stroke or a 52mm bore with the 40mm stroke, that's why technically, there's no 80cc and none of the big bore kits will make one of these a true 80cc, there's just not enough room for a bore size larger than 47mm that'll fit on these bottom ends.
There's not really enough room to bore out these jugs more than maybe 1mm but the other problem is they would need to be re plated and then finding the right piston that has the same distance from the pin to the crown, and from the pin to the bottom of the skirt etc.. yeah, it can be done, but not cheaply so not worth boring out. Putting a jug from a different engine is a lot more practical, but can also get real expensive real fast.