That particular gear may pop off for ya with out a puller. First off you will want to pry up on it with two screw drivers a the same time. Get nice wide flat ones. You will be able to pry between the engine case and sprocket. It may very well just come loose if you pry ''evenly'' is the key!
Important do not pry towards the seal behind the sprocket. Pry away screw driver handle moving away from you.
Have a buddy there for an extra hand start your sprocket nut back on but leave it very loose. Have a pointed sharp end chisel like a drift punch. put that at the center of the axle shaft so's not to damage threads in any way. Take a hammer to this punch while prying up on the said sprocket. Give it a tap sprocket should pop loose.
In this video he whacks the shaft with the nut further down you do not have this option. A puller sometimes I will gently whack the center puller bolt to get relief.
‪01 MG Steering Wheel Removal‬‏ - YouTube
There is not enough shaft and threads here. go dead center of the threaded axle shaft with your slightly sharpened chisel punch. No this trick will not work for every part on these motors. The right puller tool is the official puller!! Apr-ouched with due diligence will get your engine sprocket off. It sits on a tapered end to the shaft. Prying just right , the shock and vib from the punch should do ok for just this sprocket.