I was originally planning on getting a bare 350 block, and then getting it machined and buying the rotating assembly etc. but now I was looking on the web and saw that a few companies had assembled 4 bolt shortblocks rather cheap. Are there any disadvantages to using one of these preassembled shortblocks on a 400hp weekend driver?
Here is one that I foundWheeler Motor Sports Pro 355

 

When you take your own block in and buy your own parts, you know that everything you want done, and want in it, is correct. If you're planning on assembling yourself you can check things out to make sure things are correct.

When buying preassembled units, you are going to get what ever is in there, and unless you tear it down, you don't know if things are correct or not...

Example. I just picked up a machined block (flathead 6), they way they priced the machine work etc, I'm only saving a few hundred on me doing the assembly, but, I was supposed to get hardened seat installed in the block, what I found when I go it home was that they just reground the old seats...had I had them assemble it, I'd have never known.