518 low reverse drum

I'm rebuilding a 518 trans and need a replacement 6" 12 roller removable race low reverse drum. Can't find one new or used only the 14 roller type.
The drum from a 727 fits and the dimensions appear to be the same other the it's longer at the support so the washer and snap ring don"t fit.
The 727 doesn't use a snap ring and washer .So can I use the 727 drum ? Has anybody tried this?