camshaft for mild 340

This one will give you some lope, and still have decent vacuum.
I have it in my 340.

Lunati Voodoo Camshafts 10200703

This is what I run and agree with the other but you will need to top the guides and run proper springs. Both the summit and melling are good choices. Honestly with any cam you should check pushrod length and degree it with a quality chain and tensioner.