Cut off the entire front perch so that it is just the round sturt tube. Leave the bottom stock weld there, and the coilover sleeve should sit on it. Lay down a bead of weld if the sleeve doesn't sit so solid (make sure the weld is strong, that bead will support your whole front suspension).
I think you are supposed to cut an inch or 2 off the sleeves.
I would just drill a hole in the back with a really sharp bit. go slow, make sure it is centered, and go for it
If you mess it up don't blame me though