[redmodelt]

In a pinch the small drum parking brake with lining works. Yes you can lock up the rear wheels with the transmission brake but remember, the foot print of 30 inch tires is very small and does not take much to lock the brakes and slide into the intersection in a panic stop, been there done that. The biggest reason for adding different independent brakes, is in case something breaks. If an axle breaks, the wheel and drum come off and you loose that brake if you don't have safety hubs. If something breaks between the transmission and rear end you still have stopping power.
I have the lined shoes and AC outside brakes. I drive in town most of the time so having a little extra stopping is good. Yes I find that I might drive a little faster keeping up with traffic but I also try to keep a good stopping distance between me and the next car and watch the lights.
To the person asking about the drum size, You have the large drum.