One that screws down on the stud, and uses a handle to lever the spring. Just be sure to knock the retainer on the side with a hammer to break it loose from the keepers first.... or you can bend the tool if forced.
These tools compress the spring and LOCK into place. You can let go of them, and the spring stays compressed. It's a lever deal, and all you have to do is pull back up on it to release the spring.
One that looks like this...
You can buy about any brand of these you want from Summit.
Summit sells their brand for $41.95, a Pro-Form for $44.88, and a Moroso for $79.95
The Summit and Pro Form are cheaper copies of the Moroso unit. I have one designed just like this, but I believe it is a Manley brand. It has removed hundreds of springs, and has never given me any problems. The long handle shown on these is not built on to the tool. It slips over shorter handle. I rarely ever use the longer extension, as there is plenty of leverage without it. Plus, it fits into smaller places easier.
I HIGHLY recommend a tool like this anytime springs need changed on the head.
66 mustang real street
302 4-speed 289 heads
10.63 @ 129.3