Hopefully Thumpin455 (Todd) will check in with suggested specs.
Pick up a new timing chain set while you're in there. The cam and lifters should run under $200 from them - a bargain. Get the cam AND lifters and use GM EOS (engine oil supplement) in the oil so you don't kill the new cam - more details to follow when you're ready. I'll put you on to my favorite cam source, Delta Cams in Tacoma, WA. They get worn and the specs aren't what they used to be and besides, like Dan B said, if the 400 was not from a performance application there may be little to nothing to gain.
Putting in a used cam is rarely worth it.
