This build keeps 40 U-235 in it's internal loop to convert any U-238. It uses a SR-Latch to flip between two inserters when the chest has 0 or 40 U-235.
The issue is that it's not entirely tileable. Centrifuges down the line tent to hold on extra U-235 due to the inserters not being deactivated as the machines are working. This is fixed by outputting the converted uranium immediately while letting U-238 pass along.
Construction with beacons.
Blueprint
The single "block"Blueprint
If anyone has suggestions, please let me know!