Thanks for sharing the experience. I learned something valuable - reinforce the neck with the mating nut before applying internal force. Maybe a heavy duty hose clamp as well.
Seems like even that fancy Park tool might distort the stem if the ID of the clamp wasn't well matched to the OD of the stem.
I'm skeptical of the "drive a car over it" method. If you want to end up with the forks in plane, you'd have to overbend them past that plane so they could "springback" to the desired position. Creating a nonplanar jig with the right amount of twist would be quite an engineering challenge.
I'm a "lock in the vice then tweak to suit" kind of guy. I have a big bag of hard rubber rectangles in a couple of thicknesses, about the size of a candy bar and pieces of heavy wall pipe cut in half to form a semi-circular trough, that I can use to pad the jaws for whatever I'm trying to do.
Occasionally, I'm trying to fix something where it would be nice to have access to the kind of heavy duty rack that is used for straightening car chassis. (or used to be, now they probably just total cars with bent uni-bodies) . I tried setting anchors into my basement floor, but it just trashed the 100 year old, too thin concrete. I was thinking about dragging my workpiece out to a local railroad track, but it might be bad to have my cherry picker base and bottle jack chained down to the tracks when a train showed up.