Gear Vendors question

Hi All I have a 1971 Scamp with a 440 and 727 my tire size is 28inch and I have 391 gears
I'm thinking about going with a gear vendors unit because I want to do events like power
tour and so on. It was more of a track and around town car so any thoughts ? I an currently
going over the car and then painting

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I helped a friend put one in his 71 Dart and we had to cut the hump and raise a section right under his bench seat 2 inches to keep the pinion angle right.