Round chute is the early models. (pre-1976? or so)
Short squared-up was until '87 or so. (maybe earlier?)
Tall squared-up used after that.
If you're not happy with your blower's throwing distance, there are 3 things you can do to it.
1. Convert the chute. You can use a later tall chute, or one off from a walk behind blower. One off a WB will have cable control of the tilt, very handy.
2. Paddle clearance. Check the clearance of the paddles in the middle of the blower to the rear housing. The tighter, the better. If it is excessive (over 1/4") you can weld in new cups, or attach rubber strips with a couple of bolts and a strip of metal.
3. Speed up sprocket. Replace the sprocket on the end of the auger with a smaller one, to increase the rpms.