Any of the retrofit LA roller cams will work in the roller block, although with the factory retainer you are limited to factory-type hydraulic roller lifters. I am not aware of anybody making a solid roller lifter that works with the factory spider.
Magnum roller cams will also work if you don't need to run a fuel pump eccentric, and take into account the difference in rocker ratios when you select your cam specs (LA-1.5:1, Magnum-1.6:1).