PF26, or PF63 can be used
https://gm-techlink.com/?p=16808
Fram's "updated" website shows a 6.6L 403 cubic inch and a 6.6L 401 cubic inch for that year
PH12747 is all that's listed under the 403ci
XG10575 along with the other flavors of 10575 are listed under the 401ci
Hopefully the OP got it sorted since January