I had battled this myself with my FIA. I have decided on a close ratio toploader box with my Jag 3.54.01 rear end. This was made easier due to the fact that I already had these parts but I also have a wide ratio box if needed. I have a 66 Mustang 2+2 with the wide ratio toploader and a 3.50.01 9" rear. On the interstate hear in Ga./ Atlanta my car turns 3800 to 4200 if you just want to keep up in the fast lanes!! It really frustrates me as the engine only turns up to 6200 rpm or so. It sounds like a pack of Indians chasing me!! I went through too many senarios and went the 4spd rought because of
riginality, stronger than a t-5, a Tremic is the way to go but Pricey, and ultimately I won't drive on the interstate much. If I do it will be the short trip to get to more backroads. The shifter location played a part too. The toplaoder with the "falcon" tailshaft ( I think) was correct for my car. The mustang location was too far to the back on the tunnel. To the best of my research the set up I have chosen will have great street responce but sacrificelow end. That's why I might switch to the wide ratio later. The last owner had the same set up with a 3.31.01 and wanted a 3.54.01.. We will see once I get it running. The ERA website has some good references on trans. choices in there cars. Do you have a ERA FIA on order? Thanks, Matt.