So you want 2 go Big block...Read this first!

Actually ALL 340s were high performance, and with the exception of the 68 four speed motor, all left the factory with the same cam specs. There is NO durability difference in any 340, either. Also, nothing wrong with a cast crank until you try to make "real power".

And as far what Joe has said. Here is what I believe EVERY street a-body needs, whether it's got a /6 or a 572 Hemi:
1. Front discs brakes, 10" or 11" rear drums.
2. .890 torsion bars or larger (I prefer larger).
3. Factory front sway bar or larger.
4. Good bushings/ball joints (generally means a rebuild on an old car).
5. 15" wheels with quality tires for braking and handling.
6. Heavy duty rear leaf springs (these can be cobbled up from pieces or bought new).
7. Good shocks (open to opinion on what constitues good shocks).

Any other definciency will vary from car to car and how much abuse/neglect it has seen over the years and really doesn't factor in the current discussion. Since I believe all of the above is necessary for even a /6 commuter it should not be counted for any build comparison.

That leaves the other stuff from the original post. And the given prices are fairly accurate as to what you should expect to be able to get parts for.

Also, I have never done a slant to small block swap so I have never had the "swap" expenses in any car that I've built with a small block. The fact that my Barracuda had a slant in it when I bought it was not a problem, I just sold the engine/trans to a friend and threw out the bad k-member.