Thanks for the response Ed. The heads are already ported and I had them ported by a Ford guy that has done them before, they came out good. I was just considering selling then since they're still new, only to buy a new identical set only with the 18 bolt upgrade. Some are telling me that the 10 bolt heads will hold up fine but I've never built a blower motor before and I want to avoid problems ahead of time. Thanks, Chris