ID of Cam Towers

[Tom Oxner]

I am in the process of rebuilding my 85 930 turbo. One of the cam towers has a bearing surface the has worn too far oversize. So I need to replace that cam tower. The casting number on the cam tower is 930 105 111 1R. A fellow Pelican member has a cam tower for sale that is four bearing but has casting numbers 901 105 111 1R. Does anyone know what the difference is between these two cam towers? Thanks for your help.