Vibration right off idle

So this has been an 8 year build.

1. The trans was purchased used (supposed to be a good working unit). It did not come with a converter. I purchased one.
2. My 340 is internally balanced, using 904 flexplate
3. I have a rubber trans mount.

So I'm leaning towards something hitting the floor. Or the upper hoop. I'll take a closer look tomorrow after work.