340 cam

I would think that the Melling SPD-22 would work if. It's specs are close to the 1968 four speed cam.
DODGE Melling SPD-22 Melling Stock Replacement Camshafts | Summit Racing
The advertised numbers are a little different, but that's sometimes due to different measuring techniques of different cam grinders.
As long as the .050 numbers and lift are the same and the advertised are within a couple of degrees, I would think that would be okay. Here is some extensive information regarding the subject of 340 stock replacement cams that may give you some definitive answers:

340 cam specs?