Lol just noticed he has a diesel swap...in that case I'm not sure how they do it. I've done multiple spring changes on LS engines and that's how I've always done it. My info is no good anymore haha
Some people get pen magnets and clip the pen to the side of the head to hold the valve up.
You can also take spark plugs out and either put a large wooden dowel rod inside so the valve rests on the rod, or you can buy an adapter for an air compressor to screw into the spark plug hole and hold...