Exhaust analyzer port size

Fairly sure that that thread size is M12 x 1.25P. Best to use the Ferrari Manifold Blanking Plug 110860 (and a copper sealing washer) to block them off IMO (once you get the threads restored), and keep the (replacement) analysis tubes in the tool kit as the analysis tubes just get brittle and break eventually from the heat (and are very rarely actually needed).

 

Not sure about the 328, but the 308 fittings are 12 x 1.25 mm. The assembly is essentially a brake line bubble flair.

 

Steve beat to the post. I made mine out of 1/4 inch OD, stainless steel brake line. Hopefully, very high temp antisieze will prevent galling.