The stator is mounted on a cast iron bearing cap/cover with a 3/8" shoulder that the stator plate slides onto,this slide fit is usually somewhat tight to begin with,over the yrs with the cast iron cap expanding/contracting inside the stator ring in addition to rust the two are probably fused together.
In the past I've used the wedge/chisle method and also a tie rod separator to gently walk the stator off the shoulder although none of my eng were as badly rusted,another thing you can try is put shorter 1/4" bolts into holes you tapped in stator & with a steel rod/pin punch and hammer gently tap bolts l/r to see if you can break stator loose so it moves/rotates on shoulder then try removing stator with wedges/puller.
This may sound like a silly question-If the replacement flywheel/stator are the same as what is now on eng why don't you just install new flywheel & flywheel nut and crank eng to check for spark??
Before cranking eng check air gap between LONG trigger pin on rear lip of flywheel & pickup on bottom of ign module,should be .005"-.010",if you have spark torque flywheel nut to 50 ft lbs,reinstall flywheel cover,leave connector from stator disconnected from tractor wiring harness,fire up eng & check for voltage on 2 outside pins of stator connector,for 20A stator service manual calls for 32v+ AC@ 2500 rpm & 45v+ AC@3600 rpm,if you can get these readings then you're good to go,after that reconnect stator to tractor wiring harness to check rectifier/regular and to see if battery is being charged.