You could also have full or partial shoe separation which will only make matters more difficult..
I've had one or two that fought with me and once I finally got the drum off the friction material just fell on the floor.
Sounds like you are doing it right..
You might think about removing the actuator arm, this will let the pin slip back into the drum since it's what is holding the shoes..then as you pull the cover out the pin will slip inside and leave the shoes.
Once the cover is off you can remove the shoes and recover the pin..I did this once on my 250es when the drum wouldn't go because the shoe separated. It bought me a bit of movement and allowed me to get it apart.
Yours is the reverse design with the pin in front but it should still achieve the same ends..
Good luck..
Current toys..
1986 Honda 350X..trail bomb!
1985 Honda 250SX..my main mudder
1985 Honda 250ES..Back in Black Trike
Current non-trike toys:
1990 Honda TRX300FW
1995 Seadoo GTX
1998 Polaris Indy Lite 340(Nearly new looking)
1998 Polaris Touring 500
1998 Club Car (electric)