Lunati Voo Doo Cam.

OP, if the engine has never been touched, let's assume that your 340 has the early high compression pistons. If it has ever been rebuilt, then we don't know what pistons you have in there, and CR in that situation will be a pure guess.

The early 340 pistons protrude about .018" above deck. So, there are 2 options on the heads:

• If you select the closed chamber versions (PN 60779), you will have to use a thicker head gasket to make sure those pistons do not come too close to 'closed-off', flat areas on the new heads. A standard Felpro 8553PT head gasket at .051" thick would do that with a bit over .033" nominal piston to head clearance, AND give you the bonus of a tight quench gap between pistons' tops and the flat 'closed' areas on the new heads. BUT you'll need to measure each piston above deck and make sure you don't get much less piston-to-head clearance on any one cylinder. Running down in the low 30's for piston-to-head clearance is about the minimum safe limit for the street and with unknown parts, and any variations in parts, like a longer than standard rod length, will make the piston-to-valve clearance too tight. You don't want to risk a piston-to-head collision. You could run a slightly thicker custom head gasket if you want to bear the expense.
• The other option is to use the 60179 Edelbrock heads with the milled 'open' chambers. That head with the Felpro 1008 head gaskets will put your at about the same CR numbers. You won't have a quench gap in that setup but it will be safe from any piston-to-head collisions.

Static CR for the 2 setups above and stock early 340 pistons will be right around 10:1. Dynamic CR will be right at 8 with that cam, installed with the timing dot-to-dot. So that actually works out pretty well.

Take precautions with that new distributor and the new heads, and watch the total mechanical + initial ignition timing advance. It will likely not be happy if you push the total much past the low 30's; and it does need to be any more with that higher CR. Your overall tuning needs to be better with that level of DCR.

Depending on where you rev the engine, the standard Edelbrock valve springs are going to marginal IMHO with this cam and the lift.

Make sure you check piston to valve clearances; it will probably be just fine but don't take any chances.