To add a radio button for 7.3 to https://access.redhat.com/documentation/en-us/red_hat_single_sign-on/ you must also create the splash page using SPM2.

These instructions are old and probably outdated, but they are the best available that Matthew knows of as of 22 Jan 2019: https://docs.google.com/document/d/12Btsa5W7gDcAYIPa7z4W9ILJ6hBzGCU_BxLdY20bI_8/edit#bookmark=id.26in1rg
If help is needed, I would suggesting asking Chuck Copello. I bet he can also give a walk-through that is 100x clearer than those instructions.