Upgrade to pony interior

[gt/cs]

My mom's '66 vert needs to have the interior completely redone. I figure while I'm at it she might as well get an upgrade to a pony interior, but from what I've picked up from parts catalogs it seems the pony interior won't install on regular seats. According to the Sacramento Mustang site:

Note: Your Mustang must be original Pony Interior to install these upholstery kits. Pony seat covers will not fit over standard seat assemblies without modification!.

So, I'm wondering what this modification they mention is, and if it's easy enough that I can just pull it off fairly painlessly or if I'd be better off just buying a new set of seats.

 

[TireSmoknWindsr]

All you should have to do is get the seat foam for pony seats.

 

[TT670]

The seat foam is different and the pony frames have a different rod in the frame that the hog rings secure to. You can use pony covers on non pony frames without modification, but the upolstery doesnt pull in at all the seams the way it was done originally.

 

[gt/cs]

I'll be ordering new foam anyway so that's not a problem. Any ideas on where I can get a diagram showing this extra rod in the pony frame? I'm not seeing it in my shop manual or Chilton's. Is the difference even noticable when the upholstery is on?