The Gull arm will fit but you need the 21 shock as well.The 18/ 21 front end fitts as well,ask jeff350lc as hes fitted a 21 front end and a 18 rear end to his 16,i cant see why 21 barrels wont fit as 21 barrels fit a 18 and 18 barrels fit a 16 but you will need a 18 loom ,pgm, flywheel and pickups, the 18 loom and pgm should work with the 21 barrels.The bits for the 18 are around(and cheap) i think there is a 18 loom and pgm for sale in the classifieds and there are some 18 bits for sale on e bay uk.The 16 frame is different to the 21/28 but is looks the same as the 18,the 16 top fairing mount is different to the 18 and i think the rear top engine mount is different also, but some people have fitted a 16 motor to a 18 and only had to make up a small spacer to over come this.The 16 tank is the same as the 18 and the bottom fairings are the same.Thats as much as i know.(and the 18 exhausts fit a 16)