K Member Swap or Mounts?

I'm trying to drop a 318, 340, 360 or whatever I can get my hands on into my '68 valiant which used to have a /6, my question was do I need to swap out the k member in order to drop a v8 in there or does summit or someone else sell mounts? I'd like to swap them out so I can use solid mounts but it all depends on time/money. Thanks.
-Dakota