Buy this one:
http://www.turbobuick.com/forums/parts-sale/333704-4-1-stage-2-engine.html
I am in the midst of collecting parts for a 4.1 SII build and was planning on trying to keep it as far on the inexpensive side as possible, without skimping on the must haves like good crank, rods and pistons. Figuring $ I will have in my longblock, with intake, injectors, dist, etc, I will prob have about $8-9k, not to mention fuel system, electronics (FAST), oh, and a turbo, etc. Looking to be about $15k to be safe. And this is probably half used parts. Oh, forgot to mention the dry sump setup on mine, prob another $1,500-2,000.
I don't have a large lump sum of $, so this will be a little at a time. If you have lump sum, buy this one, or have DLS build one. If $ were no object, I would prob get a TA alum block, billet crank and rods, etc, but damn that is some serious $$$$$$$$$$$$.