[Hotfingrs]

Chris,
The opening should be the same for you current pipes. I would be willing to bet that you're going to run into problems with your new pipes. My EM was built around the same time as yours. I ordered a new set of pipes from EM, and they didn't come anywhere close to fitting. After calling EM and talking to them, I was told that during those years, they were experimenting with engine placement, and unless they had the old pipes, they couldn't make new ones. In your case switching from chevy to ford, I would have a local shop make you a set to fit the current hole. That's what I had to do.