Is base timing when the crank is at TDC with the mark on the crank at the top and the cam is at 0* with the mark on the cam gear at the top?

 

Is base timing also known as mechanical timing?

 

i believe its the same as ignition timing. When #1 piston is at TDC

 

Base timing and mechanical timing are not the same. Mechanical timing is what you described in you first post, cam and crank alighnment. Base timing is what you adjust with the distributor and timing light ie: 12 degrees before top dead. You also have timing advance that can be centifugal, vacuum or computor controlled. These are added to the base timing to give you total timing or total advance timing.