I wish I kept my notes on this. They went with the truck when I sold it. But at one time I took a 5.0 mustang engine with the dipstick in the block and had the pan off. I measured from the oil pan rail to the full mark. This is a total guess today but I think it was about 3" below the oil pan rail. I measured another engine (Explorer?) and it was about half an inch different, but not that far off.
I don't have any small blocks apart right now, but if someone does could you put together enough of the dipstick to make the measurement? That will get the height established.
Next is to know what the level is in the pan. About 6' of 1/4" clear tubing will do the trick. Stick one end down the dipstick until it is deep into the pan. drape a loop down below the pan and back up again. SUCK!. Pretty much you are trying to start a siphon. pull oil up the tube, down through the dip and start back up the free side. Keep the other free end up in the engine room. Oil (like water) will seek it's own level. It is thick and small diameter tubing so it will be slow. As long as you don't get any air bubbles in it the level at the end of the tubing will be the same as what is in the pan.
For what it is worth, this is how I change oil on my boat. No drain, so I siphon it out the dipstick. In the summer (with a little larger tubing) it takes several hours to pull 9 quarts. In the winter it has taken 24 hours. But that is 9 quarts through 12' of tubing. I have also done this to drain down overfilled automatic transmissions. That is only pulling a quart of warm ATF so it is faster. Yes, oil will siphon, it is just slow.
