572-13 heads are 13 degres, I bought a valey plate from Indy it had a large gap also so I measured it, It was 8 1/2 on one end and 8 3/8 on the other end witch caused an almost 3/16 gap I new it wouldnt seal so I sent it back for exchange. When they recived it I called them they claimed that the almost 3/16 gap was within spec, so I asked them to send me another one anyway, that was three weeks ago and I'm still waiting for it. So it looks like you all may have to live with that gap