Chevrolet Repair: 350 Timing, tdc mark, compression stroke

Question
I'm working on a 1993 chevy PU 1/2 ton 4*4, 350 engine.  I put a different motor in it and want to make sure I get the TDC and dist right.  How do you tell for sure about top dead center, I've read about putting your finger over the whole and it will blow it away, but how do you know exactly were it's at, to be right on 100%.  Will it show 0 degrees on the timing marker, that should be TDC or is this 180 degrees off, or can it show one way or the other BTDC or ATDC and show the 0 degrees on the timing marker.  Just want to make sure I get this right.

Answer
On the zero mark is TDC, both 1 and 6.
To be absolutely sure you are on #1, have the plug out, and put the mark on TDC. Then take a piece of hose....about 3/8 fuel hose works pretty good.
Stick it in the #1 plug hole, and hold it in tight so it seals pretty well, and blow on the hose. If you can blow back through the engine, you are 180 degrees off, so rotate one rev of the crank, and blow again.

When you are on TDC compression stroke, both valves will be closed, and you won't be able to blow.

Try blowing a few degrees on each side of the TDC mark if you can't blow at either time. When #1 is on compression stroke, you won't be able to blow through for more than 90 degrees in either direction.

Van