There's really no need to heat the gear to remove it. Just support the flywheel an inch or so off the shop floor with a solid base a little smaller diameter than the ring gear, and tap the gear off with a BFH and a brass drift. It will be a little stubborn, but it will move. Keep moving around the perimeter of the gear, and take your time. To expand the ring, put it on a charcoal grill and build a hot fire under it. It will expand enough to drop onto the flange on the exterior of the flywheel after a few minutes of heating and shrink to a tight fit as it cools. There are several videos on You Tube of wagon wheel tires being installed that way- - - -only they use a BIG wood fire to expand the ring.
www.youtube.com/watch?v=agGEBLUhDKEJerry