The 1968 340 manual trans used the hottest factory camshaft of all year 340's:

276/284 444/453.......all other years 340 automatic and 4 speed, including AAR/TA 340-6 specs are

268,276 429/444...

I have had the 68 manual camshaft in my otherwise stock 71 340 4 speed Cuda since 1976 and with the thermoquad I have the best of both worlds...works amazing.