The goodwrench service replacement 350 motor is a good basic engine- I bought one and installed it in my 69 elky and ran it for 4 years until i sold the car. Never gave me any problems.
They are good for about 250hp with headers & a 4 bbl carb, it wasn't crazy fast, but definetly got out of its way when you jumped on it.

I think they run about $1200, you can get one at just about any GM dealer- Be sure to call a couple of them though, as their prices will vary on the same part # engine- If you shop the price, you can get one place to beat the others price. When i bought mine i was quoted prices ranging from $1195 to $1395- I got the closest dealer to match the lowest price, and I picked it up that day- ALmost all the dealers i called had one or two of them in stock.

Someone else mentioned their warrantee- They are correct, if you change the cam or any internals- the warrantee is void.

Chevy High Performance Magazine did 6 part write up on that motor, where each month they changed out the cam & heads & various basic bolt on parts and managed to get about 400 hp out of it- Do a Google search on CHP Goodwrench buildup- You should be able to find the articles online.

If you want a crate motor with just a little bit more poop to it- check out the GMPP 330ho- This is a 350 motor with vortec heads on it- puts out 330 Hp. I think it runs around $2200- That engine would probably have to be ordered from a dealer though... I doubt most dealers will stock it since it is a performance motor.

Good luck with it!
Ben