Generally
1955 after chassis number 75299 these have anti-roll bars, you can look at the registration certificate or on the license plate where it says the chassis number.
1 pair of anti-roll bars complete with bolt, tube sleeve, bushings and washers for both sides. They sit at the far end of the anti-roll bar.
Noise in the front trailer? A common fault is precisely anti-roll bars bushings and rubber. (Sold in pairs)