I had an ANET AM8 frame, which is solid as a rock, and I wanted to re-use this and turn it into a Prusa Bear with the BearExxa axis (and extruder).
See - https://github.com/gregsaun/prusa_i3_bear_upgrade and https://github.com/gregsaun/bear_extruder_and_x_axis
In order to do this you will need Z motor mounts with a slightly different hole spacing for the lead screw and 8mm linear rod. (note, these MIGHT NOT work with the original Prusa motors, this is intended for a scratch build using rod couplers, not integrated lead screws.
Use the original screws recommended in the AM8 BOM.
You can then use all of the printed parts from the Prusa Bear and BearExxa BOMs (you might need to disable the frame slightly to get the T-Nuts/Square Nuts in place.
NOTE: The Y axis and X axis rods will be different lengths if re-using an AM8 frame they are:
UPDATE: Added the step file for the top rod holder at the request of @Wannabe245_756197 - please mirror the part for both sides.
The author marked this model as their own original creation.