If top end is your only concern, then the only real direct option is the 3:55 gears from Patrick's. Changing the tranny would serve no purpose as they all have a final drive of 1:1 unless you get an overdrive tranny, and that would require changing to an open driveline. If you do end up changing the tranny to anything newer than 1946 (for open driveline), you will need to change the bellhousing to a 47-62 truck or 55-62 car as they changed the tranny bolt pattern.
