That pretty much answers that question, Rob. It looks like 26" for the Duster and 22" for the Cuda. Now I just need to figure out if I need to find a 26" rad fan shroud that is particular to 1973 or if a shroud for the same size rad from 1969 will work. Hope so, as I can't find anything that matches a 1973 model year, with the exception of one for a 340, which was $225.
Another quick question: I have Hooker headers on the 318. What would you or are you using for small block headers on the drivers side with the last two spark plugs: straight angle spark plug boots or right angle boots?