Yes the 80, 801, and 90 all have the same cases and lower ends. The old Jonsereds company was a master at utilizing the same parts from production on many different models and sizes of saws. An example that comes readilly to mind is the entire trigger handle on your 80, will fit the 49sp, 50, 51,52/52E, 80 and 90. no matter if you use the metal lower or the plastic one and the upper trigger part will also fit the 66E and 70E but on those the lower plastic part from the 66E and 70E must be used. The only thing you have to change is the actual throttle linkage from the trigger to the carb from the 49-52 series to the larger series. The rear handle AV rubbers will also fit but I believe the larger saws use a firmer/harder/stronger bumper mount than the smaller saws. but they all will work and fit to get you by.
But getting back to the 80/90...the only differences in these saws are the P&C, and the top cover and air filtration with the 801 and 90 being the more advanced filter set up, and the stickers.
Thanks.....the reason I ask is because I can get a 90's piston and jug. If everything just bolts, I could in theory have the a '90' without the top and air cleaner of the factory set-up.
Kevin