Lead on a 408. Should I do it?

Just my two cents. If both engines are at the same machine shop why would you trust him to work on your 340 and then be leery of buying a 408 from him that he's worked on?

I'm doing something similar in my build. Non numbers car so I could do anything. I sold the 68 340 w/ X heads that was in it as a running motor on CL for $1200. I'm building a roller cam 408 w/ reworked Edelbrock heads that should be close to 500 hp. If you can sell your 340 and apply that money towards the 408 you'd be money ahead. If there's any question about the condition of the 408, have him go back through it and measure everything and seal it back up.

Don't get me wrong, I love my 340's but winding an engine up to 7k on the streets just screams for the police. With the 408 I plan on making my power down low and not drawing a bunch of unwanted attention. I agree with the earlier poster that said to make sure the rest of your drive train is up to the task. I have a rebuilt beefed up 727, new drive shaft with 1350 U joints and a Strange 60 rear end. Good brakes are must also!