The 408 would be the best bang for the buck. They are very reliable. If you wanted to buy a dart block, I'd say go for the 438. They are real monsters. I had a 438 built in a dart block with dart pro 1 heads and a very healthy solid roller cam and a super victor intake. Made 774hp and lasted 3 seasons of hard drag racing as well as lots of street duty (a little much for the street though) I know you're not looking for this kind of power, but my point is how good they hold up.
In your case, I'd definitly go with the 408. Rod angle isnt too bad and if it comes apart, you've still got enough cylinder wall to bore it again.