could it be that p/n T1140181 is just the tensioner and the p/n T1140183 is a whole kit with other parts?
do you know the price difference between the two?
I also imagine there are two for the Rocket depending on your engine color!!
I heard they were the same style on the 1050 motors that would cover the black ones I cannot speak for the 955 and 985 early speed triple motors. Either way I also heard the 1050 ones fail as sparratically as the Rocket ones so you might as well buy one for your bike.
At any rate I would suggest you first find out the parts breakdown of both part numbers then we could figure it out from there.
A couple of years back I ordered headlight extension looms from Triumph.
They sent Speed Triple cables which were shorter and had different connectors.
But sure enough the P/N's were IDENTICAL to the R3 P/N ordered.
personally I would buy the tensioner only and measure the plunger drop with a caliper or depth micrometer. If the drop was 16mm or more I would make the spacer and install it. the spacer is . is .390" diameter by .55" long which can be made from the shank of a 3/8 " or 10mm bolt.
No matter what year Rocket I would buy I would at the least modify the tensioner so it would not have a chance to realease damagine the engine and in the case of my friends who let loose the damage was highly expensive new head (due to a couple of the exhaust valves disc breaking off and well there is not much room for them when the piston goes TDC), crankshaft, pistons, and liners. All this and he had stock cams and valve springs, and pistons.