After-market Catalytic Converter for 1991 Spider

[Simon Body <body@domain.elided>]

Hi

Has anyone put an after-market catalytic converter on their series 4 
Spider? Mine has developed a loud rattle at 2000-2500 rpm and last year 
only passed the hydrocarbon emissions test by 1ppm, although the CO and NOx 
were OK. I don't want to spend $500 though, when seemingly functional units 
are readily available for $80-150.
If someone has I'd be really grateful to hear of the source and model 
number of the cat they used, and all the problems they had with installation.
Many thanks

Simon Body
91 Spider
New England, home of the 2004 AROC convention.
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