Sounds like your buddy gave you a SFI rated flex plate. It will have larger mounting bolt holes. DO NOT use this plate with the smaller bolts used on an OEM flex plate. If you insist on using it either get a different converter or have the lugs drilled a tapped to accept the larger bolts. Most lugs will easily take that little over bore and still be plenty strong. If you use the small bolts in the larger holes there a likely hood of the bolts loosening and shearing from the play in the bolt holes.
The OEM plate is plenty strong for cars up into the 11-12 second range.