Broken Valve Spring - Which New One?

My buddy broke a valve spring on his J headed 360. We don't know much about the engine. He was told it was a 380 hp 360 crate engine when he bought it, but we've since noticed that the heads are a different color than the block so we know they've been off. No idea what cam is in it, but it is hydraulic and has a decent lope at idle.

He has decided to go ahead and replace all of the valve springs while we have the tools out and to prevent this from happening in the future. We know that they can be replaced while in the car and we have an air compressor and hose to pressurize the cylinders. We have two questions.

What tool do we use to compress the springs? Can we get by with the screw type compressor available at the local auto parts store or do we need to buy the expensive tool made for Mopars?

Without knowing what cam is in the engine, how can we determine what spring to use? The ones that are in there now are single springs with a dampener.

Here's a pic for those who like to see the carnage. Thanks for any help you can provide!