Won't start

The depth of the piston has nothing to do with compression stroke or 1 turn (of the crank) "off" The piston is up at the TDC mark whether it's the no1 firing stroke or not.

There are two ways to find out, other than guessing

One was posted above, on V8's you can "stick your finger in" and feel for compression. You could also use a compression gauge

The second way "if you happen to have" the valve cover off, is bring the marks to TDC and see if both no1 valves are closed. If not, turn the crank 1 turn

Slants are more complicated because there is very little dist. movement, and the gear moves a bit as you drop it in. I guess you know there is a second bolt up under the dist.