LA headers fit on a Magnum?

I'm putting a late model 360 Magnum in a 70 Dart. I was going to use a set of Hedman short headers, but the tech guy at Hedman said the LA headers don't seal well on a magnum head. I've never heard of a problem with this before. Has anyone had any experience putting LA headers on a Magnum engine? Or are there any headers made to put a Magnum in an A body car? I'm hoping that there isn't a problem putting the headers made for a LA engine on a magnum.
Thanks,
Doug.