Just bought a 90 f250 that the previous owner lost the key and busted up the column to get the cylinder out.

I would rather not replace the column and am not worried about theft. Would it be easy to put a push button start in and bypass the key?

 

Yes but there are multiple circuits that you would need to close/open depending on function. If that's like most Fords then there's I think 2 hot wires in Run, another 1 or 2 for Accessory, and then the Start circuit. Forget the ground wire that runs to the ignition switch, it's just for the lamp test during start (turns on Brake warning light, probably a couple other things).

I've done it in a car... just used a plain aftermarket key switch wired to some relays to handle the various circuits.

 

I did that to my '88. Took an aftermarket ignition switch from the parts store, cut the wires from the ignition box on the bottom of the column and put them on the appropriate post on the new switch. I used a push button for the starter, I put one of these switches in an old Jeep and when the starter was engaged it all power was lost from the other circuits.

It's really quite simple to do, and it works like a charm for less than $20.