here ya go.. you can buy the switches as a kit..
http://www.redrider.us/518_parts.htm
PATC 727 to 518 Conversion Kit
#727518. With these four parts you can convert your 727 transmission to a 518 overdrive transmission with locking torque converter. [FONT=Arial, Helvetica, sans-serif]
Lets say you drive an average of 400 highway miles per week, at that rate you could save as much as $1000.00 per year on gas, not to mention the 31% reduction in RPM. Your new 518 will have automatic shifts into overdrive and lock-up, no toggle switch needed. Now with adjustable vacuum switch. The instructions are at the bottom of this page. [/FONT][FONT=Arial, Helvetica, sans-serif]
(11-25-06. I just saw this kit on the Internet by the copy cat competition for $1654.00.) [/FONT][FONT=Arial, Helvetica, sans-serif]
Cost $85.00 Qty 12345
Overdrive 44 MPH48 MPH
Converter Lock-Up 50 MPH52 MPH[/FONT]