Had mine done this week. I had to change my 50mm back to standard as the "Not for road use" was at the outlet end, on some older termis the stamp is at the other end, and some testing stations will overlook that.
Took me about 1hr to get the 50mm system off, then about another 1hr to 1.5hr to line up the link pipe and cans from the original set. (the springs were a right git!!).
The MoT only took twenty minutes, bike also ran fine with upgraded chip and original cans, then again was only 2 miles down the road.
Good luck..