Definitely turn the engine BY HAND, with the battery disconnected. Removing all the spark plugs and using a long wrench on the crank pulley bolt helps. Finding TDC by the WAG method might be OK for doing a rough ignition timing adjustment, or something similar, but checking cam timing or determining the accuracy of a timing mark really requires a piston stop and a little common sense.
If you want a universal tool that works on a variety of engines, thread a piece of 3/8X16 all-thread in from the top side, with a jam nut against the top of the plug shell. Adjust the length up or down until the piston stops about 1" before TDC. For small block V-8's, a 2" long bolt threaded in from the bottom with the head hacksawed off and the end rounded works just right.
Jerry
