How to install bucket seats?

I have bucket seats from what I believe to be a newer Aspen R/T or something simulair to that. I have a 73 Duster so the holes don't align well, but I figure I'll just drill new ones. The problum is the passenger side there is about a 3" gap between the bottom of the seat and the floor on one side of the seat! I'm thinking maybe finding a "C" shaped 3" bracket so I can bolt the seat on the top of the "C" and a new bolt to bolt on the the lower part of the "C" and the floor, so It would act as a 3" spacer (if any of that makes sense?) does anyone know when I could get a bracket like this? or other suggestions perhaps?

Thanks!