To follow on what Jerry said - get as much as you can from a donor vehicle -like this one:
92K Miles 6 0 Vortec LQ4 V8 Motor Engine 4L80E Automatic Pull Out Package Chevy | eBay
That way you know you will have everything that you need and it will all work together.

The $3,200 for the entire package (with a transmission) sounds like a pretty decent price.