The bearing blocks are designed to work with flanged 608 z bearings . they work great with the ACME lead screws provided with this kit .
If you have problems with z wobble i do recommend this mod. You should also replace the inner smooth rod mounts for the x axis as this will eliminate any play on the x carriage , thus making this printer very stiff and a joy to print with .
If you want to see the print quality that i get with this printer now check this out
https://www.youtube.com/watch?v=--0bgcz_bEw

The cooling fan duct for PLA needs some rework as it does not provide enough cooling for smaller parts. I will upload this part after i redesign it .
Thanks .