O.K. Here's my 2 bits. All of the original 16 mk3b's had grey painted tubs. They were painted on external surfaces only. Any internal area's were left raw. The only cars with nickel plated steelwork and polished sheetwork were the 78-82 continuation run by Lola. This was to distinguish between original cars. Also, some of the pick up points and suspension geometry was different. The later 2005 continuation cars were painted as per '69 cars. A lot of Mac's tubs are polished, but then some painted too. And it's just a good old etch primer and then French battleship grey to finish. And believe me, I know.
Oh, Marcus, riveting is carried out as soon as glue applied.