I periodically straighten parts; warped after laser or plasma cutting, assembly, or adjust angles after press brake work. Often use a 75t hydraulic, painfully slow, very controllable travel; and I did mention slow? Well, there also is a 6t arbor press with lots of travel, quicker, not so controllable.
In theory the process is simple. The key, press in small increments to reduce or neutralize stress that is causing the form to be out of desired contour. You'll only attain corrected parts by controlling movement of ram, monitoring deflection of material, or both. This time there's a pile to fix, laying a rigid scale against them, or adjusting a DTI, one by one won't cut it.
After running a few, observing amount degree of bend and travel to achieve it; I had a solution. It's a strip, attached to a pot magnet on the ram, set so it contacts ram housing with each press. It senses the smallest increment you can discern. Completely reusable, low cost, and am very pleased how well it is working. Outfitted with a stop too, maintains ram at a height convenient to load parts and zero the scale.