[Alan Roehrich]

If you convert to a forward pattern FULL manual valve body, you will not need the detent (AKA "kickdown" or "passing gear" cable) cable nor the vacuum modulator.
The valve body will run the line pressure up to near maximum all the time to prevent slippage. The shifts will be very firm, especially if the transmission is built for performance anyway. MOST full manual forward pattern valve bodies will bolt on to a stock transmission. The will retain engine braking when downshifting to second. PLEASE remember that the transmission WILL go INSTANTLY to whatever gear you put it in. If you accidentally shift to first gear at 100 MPH, it WILL go, and lock the rear tires while spinning the engine way up.