Are you going Direct Drive? The answer depends on what you are trying to achieve here. Unless I know the engine history, I don't just slap in a junkyard motor, but lot's of folks do with plenty of success. If I'm using junkyard parts it's all for a new rebuild. A rebuilt crate motor is a good way to start and you can have them put in an RV cam for a decent direct drive.
That said, the only thing a 350 motor has going for it in a direct drive application is low cost. There are lot's of better engine options for direct drive. If this is low budget and you are starting with nothing a dressed crate motor for $2K is not a bad option. Does that include everything to run, or just a long block (no carb, no ignition, no alternator etc.).