I once used a van as a headset press.
It was my first bike build, a 456 Summer Season, and I had no specialist tools. But I did have a Mercedes Vito with a big towbar beam at the back and a trolley jack. I jacked up the rear axle, put a block of wood on the ground, the headtube vertically on the wood block, the headset cup on the tube and another block of wood under the towbar beam. Then I very carefully let down the jack. The cup went in slightly out of alignment but quickly stopped arguing with two tons of van and dropped into position. The other cup went in even more easily as the first cup kept the tube more upright.
What wrong tool for the job are you prepared to 'fess up to?