Nice!
Scammells were out of my reach too, so back in '93 I built one using a LWB Land Rover as a starting point.
The rear suspension is inverted leaves allowing 12" of wheel movement up and down.
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All three axles are located with rigid A frames as on a Scammell Constructor and driven with its own prop shaft. The axles are widened Land Rover Salisburys with long shafts in both sides.
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The front axle was also suspended on an inverted leaf spring giving 18" of wheel movement up and down.
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To get 'Scammell' gearing I built a remote mounted three speed transfer box with three prop shaft outputs and a PTO.
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That was mated to a 5 speed ZF box with a low crawler first gear giving 1.5mph at 4000rpm in first gear low range, powered by a Ford York 3.6 litre 6 cylinder diesel.
I'd quite like to have it back*, as it still exists in West Yorkshire (without engine and main gearbox last I heard) but it would be next to impossible to get road legal again with the IVA test.
*This means we are still on topic....