[scottj]

Jim,
The standard spec for the 351W is stepped journals - for ease of installation.

1. = 2.080
2. = 2.065
3. = 2.050
4. = 2.035
5. = 2.020


the "C" roller bearing is 2.051 all thru and offers no advantage with regard to base circle size.

the "D" roller bearing is 1-4: 55mm (2.165) and 5: 1.968. Jack Roush developed this size to increase base circle diameter and run bigger lobes.

You wouldn't want to run a standard cast cam on roller bearings in any case. A billet or special hardened cam should be run. Comp Cams has done the most developement and has all the durability issues worked out.
Scott