what would happen if you don't bench bleed a new m/cyl? would it eventually bleed out ok on the car while bleeding the brakes? Alson what is the rubber plug for on the end of the dist block under the m/cyl? Is it a plug or something else?

The pedal in the car doesn't give you as much stroke as you can get on the bench. You'll be bleeding to no end if you do it in the car.

The plug or wire on the block under the MC is the switch that turns on the brake light in the dash to warn you of problems. The distribution block is also called a safety valve. In the event of pressure loss on one side of the system (front or rear), it will close that side and send all pressure to the good side so you can still get the car stopped.

thats not the plug i was talking about. the switch is plugged in. this is on the front end of the block and looks like a black button or plug...must be nothing!

Only disc/drum prop valves have that black dust cap, it's a dust cap of sorts. Nothing for you to do with it unless you were going to disassemble the valve, then you remove it and screw out the valve that goes there.
I've installed without bench bleeding master, and haven't had any problems (knock on wood) some times I do some times I don't.