I tried this a couple of years ago but eventually made the WRONG decision to rebuild my 350. Now it needs another re-ring, re-bearing because of some other problems so I figure I'll step up to a 383.
My research tells that I'd be ahead of the game money-wise by purchasing an assembled unit. While I have a couple of sound engine block cores and could source out all of the individual components it seems to make sense to me to just buy something that suits my criteria.
I've found a few examples:
GMPP ZZ383. http://sdparts.com/details/gm-perfor...parts/12499106
(not sure I like the piston design or the factory rods/bolts.
Competition Products.
http://www.competitionproducts.com/C...tinfo/SB383-D/
or
http://www.competitionproducts.com/H...info/SBTP376F/

As for specs I'm looking for:
Forged crank (at least cast steel),
Quality con rod (Yes, I'd accept Scat. Especially their 7/16ths cap screw forged rod),
Piston with a D-shaped dish for quench with my RHS Vortec heads.
SCR of 10:1 using 64 cc heads.
One piece or two piece rear main but no factory roller block. (I have link bar style lifters)

 

Gotta disagree about the insane costs of buying an assembled short-block. Building a 383 yourself is no worse than doing a 350, if you have patience. I also don't see the point of buying parts that are far stronger than the block itself. I've seen cast steel cranks from China survive 800 supercharged HP, and that's about the upper limit for any production 350 block. Likewise with the larger cap-screws. This just increases the risk of hitting water when clearancing, and ARP 3/8 is enough for repeated sustained 7000 RPM. Your RHS Vortecs won't feed a 383 at 7000, nor will your Comp HR lifters perform correctly at 700 with the requisite valvesprings. 2618 forged pistons are for nitrous / boost, which need heads with better exhaust flow than your RHS Vortecs. So 4032 forged for N/A, if not hypereutectic. For those heads, a $190 Eagle crank, and their 5140 rods are plenty. It doesn't take a killer build to run low 10s. Not in the engine, and not the rest of the drivetrain. If you're gonna buy some AFR 180 heads, then get you a Dart SHP 400 block, and you can shoot for mid 9s, once you also invest in a trans and an axle. The Thumpr 383 I proposed, I did because you can enjoy it for less than the cost of a new pair of AFR 180 heads. But if you can afford the AFR 180s, even if it means selling your RHS Vortecs, then you can get your 350 to run even quicker. Keep your XR276 cam for now, do some flat-tops, mill the AFRs, retard the cam, get the next-looser converter, and get to wrenching.

 

I have more options for my next build than I could list.
It's not necessarily what I need to go fast or that fast is the ultimate goal here.
What I WANT is to build one short block that'll take whatever I might intend to throw at it ever.
What I'm going to be ABLE to do might be another story.
That said, I was very happy with the performance levels from my personal bests and everything this vehicle was capable of doing. What disappointed me was that I always knew I was limited from something as simple as keeping my foot in it for some sustained WOT. Maybe a Silver State Challenge or the like. I'd like this build tp be able to survive that with impunity. I know it'll never be my 10 second bullet but that's not my objective here either.
I know a $190 crank might survive. I'm sure a $700 one will. 5140 vs 4340 rods. For the difference in cost, I'd opt for the latter. See where I'm going?
Just an assembly of ultra reliable parts.
The I can stick my heads on it, spec another cam, go low 12's at 110 mph and get 20+ mpg on the hiway.

 

It's hard to say what's "best". Especially if down the road you decide you want to go forced induction, nitrous or rev it to the moon. What might be good for one combination of future updates might not work so well for another.

 

Time to find an '01-up 6.0L, join the LSx world.

 

This is true.
I suppose it's something that I'll consider to be bullet proof at least as far as I go with it.
Forced induction, yes, I've thought about it. The block spec I have in mind (budget permitting) would provide for that.
One thing for certain though is that this next engine will be (for now) a simple NA roller cammed 400+ hp daily cruiser that will be capable of providing 10 of thousands of miles of worry free motoring. Much like my last build but WITHOUT the concern that I might drive over my crankshaft at any moment.

 

You're killing me man!
Presently, I'm involved in a 67 Chevelle that's getting GMPPs LSX 454. It's a beautiful sight (especially with a carb) but a lot of work despite all the aftermarket swap parts that are available now. That's completely outside the budget at this time.
When I finally DO get to the LS platform, I've thought about the idea of building a small displacement supercharged version. The idea being of not necessarily having the biggest "hammer" but having some HP AND getting over 25 mpg. (You should be able to see a common thread in my posts, I DO have a concern for fuel efficiency.)