ksls94

find someone with a chain wrench it goes around the pulley and holds it and it think it is 28mm but a good 1/16 will work ok

just remove the hose and with the engine running put your finger over the hose and see if it pull vac. if it does then you know thats ok but if it makes noise when you press the brake pedal you already know it is the booster. you can drive it with out vac boost but the pedal is harder to press but safe to drive i drive mine all the time that way

my 71 has a bad brake booster and it does the same thing

check fuel filter for trash of stopped up

when you pull it apart check the nut on the main shaft it is common for it to back off causing all the problems you talked about even the noise like bearing noise.

bet the clutch disc is stuck to the flywheel i have seen it before. roll the car to a safe place and put the car in 1st gear hold the brake and clutch and try to start it. it should release

even with the no compression on number 4 it should run on the other 5 cyl. try adding small amount of oil in the #4 cyl to see if the compression comes up any. my exp with being a nissan tech for 27 years tells me a blown head gasket blown only on #4 shouldn't keep it from starting need to see if you are getting spark to the spark plugs.,