If your heads are cracked then look into a set of Edelbrock heads for the Magnum.
You can use regular LA heads IF you get oil through pushrods and rockers that use oil through pushrods. There available from Comp (Pro Magnum rockers in 1.5 ratio only) Hughes engines, PRW and then the more expensive TD or Jesel brands.
Spring keeper & retainers need upgrading when you start to make a good amount of power. As in a lot off power. Think along the lines of 10.5-1 & better with cam durations @.050 of greater than 250
Stock Hyd roller tappets are OK, a little heavy. But fine for use. Your cam is tiny and OK to use the OE roller tappet without an issue.
