I would use a T-handled screwdriver and watch it as the piston goes up and down. When it's at TDC you will know. It is possible that the PO went nuts and did what they though. I have had several engines like this.
I cant remember the torque of those nuts but it's light like 6 pounds. To much and the threads of the tappet will either shread or the tappet will snap in half.