That is part of the issue. I have a new Comp flat tappet from 2010, a 280/480 and initially I figured it would be too big for a low compression engine. As I am learning here, these pistons result in a ratio even lower than I expected. The one thing nagging at me to use this cam is that I have a late 70s 360 in another car that was honed and reringed in 2002 and had low compression stock pistons, #308 heads and the Mopar Performance 280/474 cam and that one runs pretty strong for such a basic build. Given that the 360 has a .051 Fel Pro head gasket, it too must have 7.8 compression or thereabouts since they were rated just over 8.2 with a .020 steel gasket.
I appreciate the input from you guys. I learned a few things here.
With the other engines I've built for my own cars, I like to know the exact compression ratio. This engine will be sold sometime later so I just needed an estimate of the compression ratio to tell a future owner. I have very little experience with the 340, this is the only one that I have ever owned. I knew that there were differences in them depending on the model year, the balance factor, etc.