they're fine to sit on the speed limit, but do make a bit of noise. The K has a 3.765:1 diff ratio, the 1000 leyland probably had a 3.44:1 diff ratio. This means that the engine is doing 4100rpm at ~100kph in the K, but the leyland was only doing 3750rpm at the same speed
They're tough motors, they're not stressed about revving a bit. We're spoilt with modern cars, having more efficient engines, making more power, meaning they can run higher gear ratios and overdriven 5th gears... people don't expect to 'hear' the motor working or see the tacho needle anywhere over 3500rpm, even though they're happy to run at 6500-7000rpm all day
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