They are closely related but not identical. The GT6 uses the same basic 4-speed all-synchromesh 3-rail design as the Spitfire, but with different internal ratios and a different bell housing. Fitting to a Herald or Vitesse also requires modification due to the gear lever aperture position. Always confirm the application before ordering.
Yes, reconditioned exchange gearbox units are available for both non-overdrive and overdrive GT6 specifications. Units are supplied without the bell housing, gear lever and ancillaries. Rimmer Bros, based in Lincoln and specialising in Triumph parts since 1982, despatches reconditioned units worldwide.
Yes, the Laycock D-type is the correct factory overdrive for the GT6 3-rail gearbox. Fitting one to a non-overdrive box requires the appropriate overdrive mainshaft and adaptor plate. See our GT6 Overdrive section for compatible units and components.
Yes, overhaul and reconditioning kits are available covering the GT6 across Mk1 (1966-68), Mk2 (1968-70) and Mk3 (1970-73) production. Kits typically include gaskets, seals and bearings. Check individual listings for exact fitment, and see GT6 Clutch for related drivetrain components.