I had my car out on the highway yesterday and a person gets tired of 3000 RPM at cruising. I have a 1970 with a 351C with a FMX and 3.70 gears. How much is a kit to convert to a tremec and how much cutting and drilling. My car is one of six left so I'd like to be gentle. Will the new shifter go though the old hole? Will the firewall or floor have to be cut?Which kit is best?