RustyRatRod's Guide To Hot Rod Bliss

Converting from a 6 to an 8 is a bit of an expensive route that you want to do and accept the added costs. Rusty's comments are for "In general" approach.
It's almost mind blowing you mention it.

Your example of engine swapping doesn't apply. Rusty is not addressing every approach. Just the basic idea and parts. When you bring up engine swapping, it just seems like your trying to be cute and throw a wrench in the works on purpose.

The cheapest way is ether a donor car for peanuts or a swap kit. And then Attend to all the issues reguarding the swap that a donor car would have had. This topic is well covered over and over and over again for /6 to small and big blocks, small blocks to big blocks.