I'll see your rare Foden Will Shiers....and raise it. back in the mid-90s Freightliner/Railfreight Distribution had Foden make them a brace of Detroit Diesel 60-Series engined 4000 Series tractors. As far as I recall it was just two but with different ratings and they even looked at different Eaton gearboxes--a nine and a 13-speeder. Along the way Commercial Motor  roadtested this one around our old Scottish test route including the severe gradient section. This shows it just climbing Kiln Pit Hill on the A68 (AKA The Valley of Death).

But the real question is what happened to those 60-Series-powered artics? Who out there amongst Biglorryblog's anorak army knows where they went...?