PCV or Breather caps???

I had a Ford 351 4V CJ that I bought very cheep from the owner, he complained that the front and rear intake seals keep blowing out. I took one look and knew what the problem was, he had the stock oil breather cap on one side and had put a spark plug in the PVC hole. No problem at idle but 1st time he revved it the seals would pop out.