Ive used the rubber sandwich type in tight spots. If you can get the old ones out without taking the engine out, the rubber ones just slide in and then you tighten the nut and it expands and seals. They have worked great on 2 different engines Ive helped family out with. There was no way I was taking the engine out of my sisters 89 buick to replace core plugs, which I wouldve had to if I chose traditional core plugs.

Never used them on a nice car though, they are a little goofy looking, but they work