Hi @mreedks,
I’m happy to hear you like the OJS 3.1 interface! Other users agree that editors should be able to send attachments with the submission acceptance email and it has been filed as a feature request ([OJS] Editors should be able to add attachments to the Editorial Decision message · Issue #2438 · pkp/pkp-lib · GitHub). Feel free to add your comments here and follow progress or contribute to development of this feature. In the meantime, the only workaround I know is to send a follow-up message in Discussions that includes the attachment. You could also try customizing the template file (see [OJS3] Mail Attached Files - #5 by Cristhian_Andres_Rey).
Best,
Amanda Stevens
Public Knowledge Project Team