Valve train?

[sixpony]

I recently pulled my engine to replace the weeping seals/gaskets, since I had a broken exhaust tab on the head I decided to replace it with a 78 fairmont head, when I sent it to the machine shop I was told that it was cracked though none are visible to the naked eye, when I pulled it off the donor it did have a lot of carbon around the bolt head behind the carb, tempted to have it checked again, seems this machine shop sends back a lot of "cracked" heads. Probly just use it for a core when I get the bucks to buy a rebuild and do it right. In the meantime I tacked a stud on my old head and will use that for a while. The rocker shaft off the late model is a little different in appearance from the 66 model, would it be wise to use the 78 shaft on the 66 head or should I just stick with the original for now, had no problems with the original except for a lifter that would stick and make a racket occasionally , probly from the tremendous amount of sludge I found in the motor (cleaned it out the best I could) I know a rebuild and a hot tank are in order but it runs well, uses no oil and I just want to get buy till I can afford to build one right to replace it! :thanks:

 

[JackFish]

The rocker shaft off the late model is a little different in appearance from the 66 model, would it be wise to use the 78 shaft on the 66 head or should I just stick with the original for now

I'd like to know in what way they are different.
Does the earlier one have adjustable rockers?
I'd probably use the one that had the best shaft.
If you push/slide the arms sideways you can see if there's any wear on the shaft.