I've done litterally HUNDREDS of these...
I set the ring gear on a kerosine heater and put the flywheel in the fridge or freezer.
Ring gear will expand at about 100°F to 150°F and you don't have to worry about cracking it from uneven expansion like you do if you use a torch and don't keep the torch moving...
200°F in the oven for about 30-45 minutes so it gets good and warm all the way though and it will either drop on, or you can drive it on with wood block and hammer.
If you freeze the flywheel the same amount of time, I GUARANTEE it will drop on with very little coaxing (IF ANY! Most just drop on!)
Make sure the ring gear is SQUARE on the flywheel!
Use a brass punch and hammer or wood block & hammer and make sure it turns true on the flywheel before you do something still, like eating the starter drive gear up!
Once it's squared up the best you can get it, then tack weld it in place...
Lot's of people don't think that's necessary.
But when wheeling, we've had to use the starter to get us off obstacles when the engine wouldn't run (too off camber for the carb to work)
Hard on starters, but it works!
If the ring gear slips on too easy (which it doesn't sound like it's going too),
Or you slip the ring gear on the flywheel trying something stupid like we do
you'll wish you had put 3 or 4 spot welds on that ring gear!
COUNT YOUR FLYWHEEL TEETH!
AMC FLYWHEELS came in TWO FLAVORS,
154 teeth, and 168 teeth, and if you run the wrong gear, you get to do this again since the starter drive gear will eat up your new ring gear!
If you have the 154 count, get a starter for a I-6 engine.
If you have the 168 count, get a starter for an FSJ with 360 CID engine.
Both will fit your block, and the starter drive gear will be correct...
I need to sober up now... So good luck!