LateArmLive,
The Rolls Royce trials I mentioned - I'm pretty sure it was ZD402, painted black to look sexy - were with the 1161 engine, it was quite a while ago, probably 1988/9 ish.
I believe a standard engine was refitted afterwards, as there was a major effort to prevent the 'fleets within a fleet' situation which had come up with frankly most R.A.F. aircraft, everything from hand-made panels to various avionics fits.
Unfortunately I don't have any photo's now, largely as the trials were not conducted at Dunsfold.
I'm sure there are Test Pilots or Flight Test engineers out there who can put me right.
P.S, I was having a particularly dumb moment re. IAS !