Welcome Mike! You are mixing up a couple things here. There are generally 2 Ford chassis upon which Class C's sit, the E350, and the E450. Also generally in the E350 chassis there was the 460CI V8 until 1998ish when the 6.8L V10 became available. The 460 V8 was replaced with the smaller displacement 5.4L which is available in the E350 chassis around that time frame. So what you were mixing up was engine size vs chassis. The E350 is generally used on the shorter length Class C and the longer Class C's were built upon the heavier duty E450 chassis. I say generally because I have seen some smaller Class C's that are built upon the E450 chassis. Prior to '97-98 I'll defer to someone who knows more about those years.
To add to the confusion, the chassis could be a year or more older than the house part of your Class C. A 2000 Class C could have a 1999 chassis.
I am completely ignoring the GM chassis or Dodge options as I know little to nothing about either of them.