So I'm getting ready to rebuild a 340

Ryan, you asked about what HP will that give me and the poster submitted no info that would give any clue to that.

My question to you is what kind of HP are you wanting to get?

Here are s my suggestion for a daily driver with or without a 4.00 stroke.

750 cfm
RPM intake
Edelbrock heads (some porting for the stroker)
1-3/4 headers into a 2-1/2 exhaust, an H or better yet, an X pipe exhaust system.
Compression NOT exceeding 10-1.
A cam that has an operating RPM in the area you cruise in.
(What kind of cam are you wanting to run? Hyd. mechanical, roller?)

Now, what trans, rear end gears and tire size do you have?
And how heavy is your car.