Chambered Exhaust

Has anyone ever run across a 65 with chambered exhaust instead of mufflers? Back in 65-67 I worked at a large Ford dealer and told the sales manager to order a hi-po with every option available for myself. It was a very early 65 car, as it was ordered long before they were available for public sale. (the 64 1/2 generator cars were already out). It arrived with chambered exhaust, which I later cut off and replaced with headers and custom exhaust. I worked on every hi-po that went through the dealership and never saw another system like it until it appeared on Camaros a year or so later. Last summer, I talked with another old Mustang guy said he had one too - so I thought I would ask here.

Thanks guys. Several hi-po owners I talked with thought I was mistaken. I don't know why I didn't search here first.