The best way I found was to rotate engine by hand. When compression is felt (rotating will get hard), Push down one of rockers, for each cylinder, one at a time. 2 of the 3 cylinders will not affect ease of rotation. 1 cylinder will cause rotation to get easier and you may hear air excaping from cylinder either thru exhaust or intake, it depends on which rocker you push on. Then you know that that cylinder's piston is on its way and close to TDC.
On my 3T80 there are marks for 1,2, and 3 TDC, if yours does to, that will help.
Be advised that this proceedure is how you adjust lifters too! And is how I determined I had poor compression in 2 cylinders, prior to my rebuild. While rotating engine it never got difficult to rotate by hand, until #3 cylinder came up to TDC. Implying that 2 of the 3 cylinders had poor compression.