Check out
http://www.hothemiheads.com/. They have a lot of the parts for the early Hemi's. Do make sure you get parts for a Dodge, because the Chrysler, Dodge and DeSoto hemi's swap ZERO to very few parts, depending on which ones you're talking about.
I know the crank keyways on the early hemi's are a different size. You can use the later balancer's with a step key, but I don't know about the timing chains, and it might be model specific.
For example, the 241/270 Dodge hemi's and poly's can use a later 318 distributor with no modifications. Drops right in. I have one in the 270 in my g/f's '55 Coronet because the points are less expensive and easier to get than the early ones. If you're running 12v, you can even use the later electronic dizzy's (we have 6v still). But on all the other Hemi's the distributor shaft has to be changed, wrong length.
