Your trailer is heavier than mine.
At 6500 your load is about 150% the weight of your truck. Trailer brakes are real important because your load will want to push your truck around. With 6500 behind a 4000 (3700 curb, plus driver and whatever) pound truck, your combined weight is 10,500 against a rating of 6900.
When your trailer brakes work you are probably fine.
If this is just local hauling and not at highway speeds, the stock engine and transmission can probably do the job, though not with great speed.
It's still the brakes that are most important. Compare your brakes to those of the new full size with a V-6.
I may seem to have a one-track mind here, but once you've been pushed through an intersection by your trailer because your truck didn't have what it took to stop the load you'll preach the same message. While I'm a strong believer in trailer brakes, I also believe you want enough brakes on your truck to stay in control when the trailer brakes fail.
The hardest part to find replacements for in your current brake system is the drums. Since in '54 you have Bendix brakes, one thought I have is you could upgrade to sintered metal linings and improve braking performance. Of course the down side is your drums will wear quicker...
