Hot Rods Morbec build-up help needed

I finally have a set of Morbecs. Still in TX. Looking to fit 15” shells/hoops/rims as the wheels are 14” at present. Some 60's wheels used the same centres with interchangeable shells. Center id needed is 12” rather than the readily available Bart/Speedway 12 ⅝” centers. So, who makes or can make 15" shells with 12" centres? Any NOS 60s shells/hoops around or what is readily available that I can adapt? I need 2 x 7" and 2 x 8". Any advice gratefully received. Thanks.