Not sure of thread size but it will be BSF. As far as I know there is no way of dating machine from serial number. However I know from information on the old forum that engines have a date stamped on the flywheel. Will have to have a search to find exactly where.
The old forum will eventually close and all content will be saved as an archive on the new site.Please start all new topics on here and not the old forum. The more you add the more there will be for everyone to read.