Adapting Frame Rails - Help

[Karter18]

I bought some Recaro's and they have seat brackets on them for an earlier car. I unbolted the rail assembly and I am trying to remove the vertical support. It appears they had a spot weld on the bottom and four what looks like a stamping to put them on the rails. I drilled out the holes and ground the weld off and no luck yet. Any suggestions from the guru's on here is appreciated. Photos below.



I am trying to separate them as it looks like they will bolt right up to my 1987 mounting points.