Its the older 2 piece seal, will my '91 350 TPI heads and intake bolt to it?
Would it bolt to my transmission?(700r4)

And whats the difference between the gaskets, rings and bearings?
http://www.jegs.com/i/JEGS+Performan...0081K/10002/-1
I wanted to buy something like that(both engines need a rebuild), but its only for 67-86, Jegs doesn't have any for the 86+

Heads and intake will bolt to it, as will your 700. You will need a new flexplate, or one that is balanced for the earlier crank. The later crank, '87 and later, is externally balanced because of the 1 piece rear main seal.

As for gaskets, the pan seal on the pre '87 is a 4 piece deal, where as the '87 and later block has a 1 piece pan seal. That kit should work for your new engine, however I used to purchase my main and rod bearings separately, in case I needed different size bearings (under or over size).

As mentioned, you will need a crank that matches that block, as well as the flex plate/flywheel. Your starter may or may not work depending on the bolt pattern that the block is machined for, as well as the dipstick.

The benefit of using the later block is the 1 piece rear main seal, 1 piece pan gasket, and (usually) a roller cam.

I've been thinking about the pro's and cons, I don't think I'm going to making enough power to really need to the 4bolt mains.
Thanks for the help, you answered everything I needed.

Honestly, if I were still using a SBC and I needed a new block and I came across a 4 bolt main, I wouldn't think twice about using it. Pretty much everything that I mentioned would need looking at anyways, but I mentioned everything because I ran into those same issues with the first 350 that I built years ago. However it's issues like that which drive the price up on a build, and I don't know what your budget is. May be a concern, perhaps not.

Yes, unless you're making near 600 hp and spinning a stroker to 7000, 2 bolt mains will do just fine.
I've been spinning my 350 in the Impala to 7100 for 4 seasons and making 660 hp on the 100 shot with stock 2-bolt mains.

napa carries a one piece oil pan gasket from felpro for the older blocks
i have one on my engine cost was 27$'s

The performance advantage of a roller block with roller cam more than outweighs the number of bolts on the main caps. Bonus is that you can use your old flywheel or flexplate, and when/if you move to a T56 you can use a stock flywheel instead of a $500 conversion one.