I improved my Prusa i3 MK2.5 (originally bought as an MK2) with alu profiles (30x30) and plates like the MK3 has.
But then the problem occured that I needed slightly different plastic parts (the ones I uploaded) after I mounted the alu profiles and the alu front- and backplate.
Apart from filing off some material and drilling holes in the frame the y-axis-motor holder needed a conversion to be able to mount the end stop. Thus the y-axis-belt holder had to change because the end stop was in a different location (18mm further back).
Here are the steps you need to follow to upgrade your MK2/MK2,5 to the alu profile version:
1.) Print the 2 plastic parts
2.) Get the alu profiles / front- and backplate
3.) Drill the holes in the frame
4.) File off the material where the heatbed-carrier slightly touches the frame
4.) Mount the alu profiles / front- and backplate
5.) Attach the y-axis end stop
6.) Reattach the other parts like heat bed etc. again
If you have any questions feel free to ask.
Thanks to gregsaun for his bear upgrade instructions.