thom;

regarding brakes, maybe you have a drum or two out of round - this will
really make them lock up hard at a certain pedal position. you might be able
to isolate it by doing a series of stops with the handbrake only - at least
you can differentiate front/back. Are you sure you a re getting the right 
shoes for that old bag of bones? If the shoes arent radiused to the drum

correctly your braking will be terrible. If you have a hydraulic problem i
think the only way you will find it is to put pressure gauges on each
wheel, not a cheap proposition unfortunately, but otoh yu want you brakes
to work as well as anything else on the car, right?

regarding your your engine, i would do a cold and warm compression series to
see if your p/c/r and valves are doing their thing. For running at speed,
carbs (esp the 28) are operating in their simplest mode - its hard to
imagine something wrong here - maybe take the top off the carb, unscrew the
main jet and check forplugged holes?  cleean with air, not wire !!

lots of silly things to check too, choke coming off all the way ??

i would probably do a compleat tuneup starting with valves, ignition, then
turn attention to the carb. Btw that 28 carb isnt the original is it?
I presume ut was running better with it before so you know this carb
works ....:-)