I've raced N/SS in the past and will again. I think the biggest reason for more Mopars is period engine availibility. Ever tried to find a 409 or 427 FE block? Though 440s are becoming scarcer there's still a lot out there. Pontiacs aren't that tough to find as well. You can always use a 390 Ford, not much power though. Yes there are aftermarket blocks. A low 11 mid 10 440 can be assembled for less than the rest. That coupled with the fact that Mopars are just plain cool. My dad was a stylist at Chrysler. He worked in B-Body design studio in the early 60s. The designs of the 63 and 64 Plymouths were done by his group. He also designed the triagular shaped Dodge emblem.
Doug