Would have thought so, the MC from an early non abs clio is around 1mm smaller dia piston than the 172 cup/Ragnotti MC (both have 2*m10 & 2*m12 ports). Presumably be worth doing a little reading around the effects of altering piston size.
The one on the cup racer is 4*m10 and is around 1mm larger dia piston than the 172 Cup/Ragnotti MC. The servo they run is also slightly larger than the rhd road cars - dont know about your lhd. Can measure if you're wanting to know.
Don't see how blanking the two redundant ports would be any different from if you were blanking one to run a bias valve to the rear calipers.
Do you have to keep the ABS for Hollands equivalent of the MOT? Surely just be easier to take it out and make new lines with a bias valve?