I do not actually know what you are anticipating fitting (flexi pipe catalytic converter ??????) but I have, approx 100 miles ago, fitted a replacement Catalytic Converter to the right side (offside/driver side, Bank 1) on my 2005 S Type 2.5 Facelift. I actually fitted a replacement that is to OE standards/quality (a solid pipe and Cat. Conv.). The job was reasonably straight forward and easy going. I did also make certain I had a fitting kit so as not to have to mess around with old, rusty and hardened clamps and manifold joint. The OE standard spec pipe and CAT was very precise in manufacture and was in no way difficult to make fit. It was an exact fit.
As previously stated I do not know what the "flexi pipe" is, but I would be concerned that it is by definition introducing two extra joints to the system and have no idea how accurate/easy the fitment will be.
Best Wishes with the fitting and Regards, John