It depends on how much your mini-tubbing! If its a 3 inch mini-tub you'll likely have to narrow the the seats some on coupes. I've heard convertibles actaully have a smaller rear seat design and usually get by unscathed in mini-tub projects. I'll soon find out as I'm mini-tubbing my own 67 Convertible currently. -Chris
Dont forget the gas tank hits the mini tub if you use the DSE mini tub kit. You'll have to narrow the tank 2 inchs on either side if you use the factory tank. And yes,with the coupe, you'll have to narrow the seat or do what I did. I cut out 3/4 inch plywood forms covered with factory looking carpet that I made from Cardboard templates, Then I put two subs in the "back rest". Nobody rides back there anyway.
Hope this helps some.