On a 1992 L98 350, when the timing mark on the cam sprocket is at 6'o clock and the crank mark is at 12'o clock the #6 piston is at TDC. With both marks at the 12'o clock the #1 piston is at TDC.

 

#1 is at TDC either way. With the crankshaft timing mark straight up, #1 is TDC. That's all there is to it. Whether the cam mark is up or down only affects what stroke it's on (compression or exhaust.)

 

A little known trick (to not getting the distributor in backwards) is to install the cam with the dots in the 6 and 12 o'clock positions. Then, rotate the crank 1 turn. That will put cylinder 1 on the firing stroke. If you leave the dots "up and down", you'll be on the firing stroke for cylinder 6 and need to turn the distributor 1/2 turn and install it on cylinder 6. So, if you have been lining up those dots and wondering why your distributor is always 180 degrees out, that is the reason.

The cam gear has twice as many teeth as the crank gear, so every turn of the crank will turn the cam 1/2 turn (which leaves the dots at either 6 or 12 o'clock on the cam gear when the crank is at 12 o'clock.

Hope this helps!