Look at intake valves from a '54 to '60 Ford six-cylinder. Right length, right stem diameter, correct locks - but bigger diameter. Also they are flat instead of cupped so will add slightly to your compression ratio. These are readily available at an affordable price. Application is '54 - '60 223 cu. in. six cylinder. Head diameter 1.780" Granted, not a huge diameter increase but many people in this area have installed them and all say it made a noticeable performance improvement while remaining streetable . TRW 2056X or Sealed Power V 1115.