i've checked my tach at many different speeds linearity is fine, this is with a rabbit gti tach converted with reg cheese mans directions, which i believe just converts the gti tach over to match the mk2 td clusters. usually when i put the clusters together u can just swap the diesel center led section and membrane over to the gas cluster then everything plugs together and works as normal. this isn't always true tho. the 81-84 rabbit stuff is the easier to mix together, cabby jetta clusters are pretty easy too if u get two that are from similar years, the mk2 stuff has many different styles so some are easy some are a pita. when i make the clusters i want it to look like it came with it from the factory, so proper symbols and such are important to me, but not everyone cares about those types of details. the dakota stuff is a great option tho, u can easily swap the membrane and lights over, and then just wire in the dakota converter