Way, way back I bought Armours' siamese pipes for my RGS and twin pipes for a Super Rocket.
The siamese needed the short (left) front pipe extending at the head port by about an inch. The chrome has been OK.
The twin pipes hung in the shed for over 15 years. When I recently fitted them it was necessary to extend the left hand front bracket, in order that the rear of the downpipe cleared the primary chaincase. The chrome showed corrosion due to pitting but, after a good polish on a rotary mop, looks quite good.
It's very worthwhile if you have a welder and are not afraid to use it.