Heater motor

My heater motor went out in my 1978 cj. I need to replace it but was wondering how much of the duct system do I need to tear out to get to it? The motor sticks through the firewall but doesnt come out that way. There is a round circular pannel on the ductwork that might access the motor, anyone know? Also I heard of people replacing their motor with a stronger GM one. What type motor and for what type will work in a jeep? Thanks for any input.
Glenn.

Thanks for the info. I was afraid I was going to have to do this. My Jeep is fiberglass and the dash bolts wont come out. The pieces that were molded into the tub broke loose and just keep turning. I'll figure something out.
Thanks Glenn.

I installed my heater motor today. I put one that was for a 1973 Full size Blazer 350 v-8. Another Jeep board member gave me the link to to the fix. It wasn't too bad. The biggest issue was cutting the hole in the firewall bigger. The GM motor was 3 1/4" diameter versus the factory jeep motor is 2 3/4" other than that everything matched up perfectly. This motor moves allot more air than the factory motor. My jeep is fiberglass so I think it was easier to cut the hole bigger than it would have been a metal. I only removed the card board glove box and dropped the duct assembly without taking the dash out. I didn't even unhook the dash cables. It took about 2 1/2 hours to complete. The other item I had to remove was the battery holder.
Glenn. ;Dl one.