Rhine620

So I'll be driving then my brakes will start to gradually lock up until it won't move then have to get out and open the brake bleeder vavle on any tire doesn't matter and it will start rolling again could this be the brake booster? And also when I apply pressure to the brake pedal when truck is idea long it will die?

Yeah it is the donor truck way to much body work and I like the original truck a lot more then this custom Frankenstein

The truck I'm looking at buying is a 74 with no motor in the truck I have right now I think is a 78 bit I don't know I have no paperwork on it and there is no vin to be found nor does it have any smog equipment and the body work that has to be done alone on it would take forever but it runs pretty good other then the carb needs a rebuild and the transmission shifts smooth so I was wondering if it's pretty easy to swap the entire drive train from the 78 into the 74 that currently has a automatic trans and how do I post pics on here

So I'm wondering how difficult it is to change from a automatic to manuel trans in a 74 620 I have a donor truck with a L20b and 5 speed trans any suggestions greatly appreciated