They are two separate parts and the backrests are no longer available from Triumph dealers unless old stock. There have been a large number of factory backrest versions that will fit over the years.
Standard, Touring (not R3T), Classic, Premium, and a Gel version to match seats besides about 5 vinyl variations with some of those.
SISSY BAR BACKREST - STANDARD A9701144
SISSY BAR BACKREST - TOURING A9701145
SISSY BAR BACKREST - CLASSIC A9708117 and later A9708177
It is also likely that SOME other Triumph models passenger backrests will have the same four hole rear mount boss spacings. Eg. T2300348, from Thunderbird (early 865/900 triple), Adventurer, America and Speedmaster carb and EFI models.
I have a New old stock one on the way here. I have checked it has same 4 hole pattern and I have measured spacing on screen for a match. If it is not exact I will find a way.
Here is the Sissy bar and rack.
Triumph
A9738070 Triumph Sissy Bar & Rack, Tall $281.76 - 2WheelPros
Product Description
Requires a sissy bar backrest pad p/n A9708177. Pictured with the sissy bar badge p/n A9738002, not included