The SD455 heads are so rare and valuable today that it's a shame to port or shave them in any way. The original SD455 was designed with the RAIV cam. The prototypes used the RAIV cam, but couldn't pass emissions (there's a whole story about that that's pretty cool)
The skies the limit if you want to build it with "secret" parts. Aluminum rods, lightweight pistons, hydraulic roller, it really depends what you want to do with it, and if sounding totally stock is a priority.