I've done some research today and been under the car to measure it. The manifold has two Lambda ports which as I understand makes it a MIllTek system??
The ID of the donut would need to be 57mm which I can find on eBay so I might get one from there and make some sprung bolts at work. Failing that I did speak to Pumabuild today and the guy I spoke to said he might have some knocking about.
Like a lot of parts for this car, it's been a lot harder work than I thought it would be