Yo Eliems
I have 16K miles on my Crane 359351 hydraulic roller cam and it has been great in the 521. Highly recommended! They have three other grinds now for your choosing pleasure, one hotter and two less aggressive
It's a bit expensive, but waayy worth it.
A caveat: be sure to buy Crane's steel distributor gear
and make sure it is correctly installed! Don't ask me how I know this...
Tom
PS: EDIT: Be sure you get the correct springs for whatever cam you buy. The triple springs for the solid rollers are good for 3-5K miles!