Thanks all for the replies,
I received an email from George evans this is the guy that did Ross's engine rebuild. He advised me that the clearance for both the inlet and exhaust is .018 of an inch which is 0.45mm. I have advised my workshop to use that setting, George has rebuilt many Jalpa engines over the years and I trust his judgement.
As Jalpa_Mike has mentioned there are a few different figures around I also had the
Inlet: 0.45mm
Exhaust: 0.5mm
settings in my hand book, from memory the Urraco 3000 engine workshop manual has the settings both at 0.45mm

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Jalpa ELA12175