suggestions for my 340?

The best way to go about modifying anything is to do the entire system. If you start tinkering with valvetrain stuff, go with bigger ported heads if you want more RPM, port match an intake with large runners, like the Edelbrock RPM, be sure to center the intake with a witness mark on the cylinder heads, before bolting it down. Don't trust the index dowels on the front and rear to go into the holes and make the runners perfect.

The camshaft changes everything. If you run another cam in it, the power range in RPM changes and you need to make sure that your stall speed is good with that range, as well as your rear gears.

There should be a tag on that differential that denotes gear ratio. If not, check the ring like rumble suggests.

Edelbrock heads are nice, but they aren't cheap and should go on an engine with good quench, good pistons and good compression, otherwise you aren't getting your money's worth.

J heads are open chamber. Some late X heads are the same, regardless of 1.88 or 2.02, the chamber shape is what counts most. Bigger valves only help when you have larger runner volume up to the carb, matched and centered.

You'd be better off with a set of aftermarket iron heads, than edelbrock stuff, or a set of true, closed chamber X heads.

One silly question, if you aren't certain of numbers on the intake, have you checked to see if you are running a 340? I wouldn't trust just cylinder head letters or numbers. That engine has been apart and out, by the look of the Chrysler Red paint on it.