68 Cuda P/S converting to 73 K-Member with Manual steering

I don't think the coupler is specifically the problem. Manual and power steering columns are different lengths. Did you say you got the 73 steering column? If so, you just need a 73 manual coupler (but I think they are all the same). If you didn't get the column you might be able to get an adapter (I forget which shaft is longer -- obviously the adapter only works if the shaft is too short, not if it's too long).