340 Vs 360

I was talking to an older gentleman that I've known for years about LA blocks. He is very familiar with Mopar, as he is a retired mechanic and owned many Mopars.

I told him of my plans to do the 318 / 360 swap. He suggested a 340. That surprised me. I am not sure if he is as familiar with the 360, as he has been retired many years.

But this got me curious, what is the basic difference(s) between the two? I know that for the guys restoring a car, an original engine is the way to go, but what about nothing other than a performance upgrade?