A couple of items that haven't been referenced thus far, your 880 block with a 1 piece rear main seal requires a crank designed for a 1 piece rear main seal. The camshaft and timing set for that block needs to be the correct set and cam for the block. It is possible to use the wrong crank, cam and timing set, but it requires a bunch of machining and/or special parts that are not needed.
On the positive side, new parts for each setup are readily available and the factory roller cam setup is the most desirable as long as you stay below .550-.560 lift (I believe those lift numbers are correct - someone can correct me if I'm wrong.). Regarding heads, Vortec heads can be put on any SBC block, but they require a specific intake, and if you want to use facotry valvetrain, then they require self alighning rockers or standard rockers with guide plates.
Personally, I would not consider using a set of known good heads and all of the valve train components to go with them. They are expensive to rebuild and modifiy to handle any type of performance camshaft, and at the end of the day, they are limiting UNLESS a stockish build is all your after. Buy a set of assembled FloTek aluminum heads or assembled Promaxx in the area of $750-850 and be miles ahead of any stock SBC head. From there the price goes up, but many decent aluminum heads are available for less than $1500 per set assembled.
What else do you have with this block? Lifters, crank, rods?