I would like to run a Perfomer EPS on my 89 heads, but none is available. I guess I don't mind enlarging the center holes on a new new intake, but how do you then get the bolts to hold square on the intake ??

 

You can either use a spot facer in a mill to machine the deck of the intake at the angle you need, or use 15° structural bolt washers (the kind used to bolt to/through structural I-beams) and file them the few extra degrees to get the angle at a perfect 18°.