roll cages are ok, same as stripping out ur car, never seen anyone fail nct due to them and seen loads go through with, so they should pass, the only thing is if you get bad garda (we all know they exist!"!) if the check ur insurance and its not listed!!! mate got his twin cam taken and insurance cancelled due to this.....
also according to garda press office u are not allowed use harnesses in a road car, if you do not use oem seat belt it is like driving without one.... wonder is you use both?? (",)