ok been a long time since i used max but the simple workflow should work
- set the biped to the correct height in the figure settings and scale the mesh to fit, then use a xref modifier and collapse the stack
- skin mesh to biped using the “Skin” modifier
- set the biped into the T-pose and export via fbx
- import into ue4 and create a new skeleton
- now you can set-up your skeleton to re-target the Epic anims to your biped rig