This is a follow up post. I did some research and found a very informative site here: http://www.timesert.com/
It gives instructions on how to install Timeserts, what sizes are needed for certain engines including Vanagons.
I don't think I'll need to go to the oversize Timeserts, which are recommended in cases where the thread is damaged in the aluminium block.  If that is the case, then I would also rethread for the larger diameter insert.
I will certainly use the red Locktite.
By the way, it was a new copper washer that was used and is now stuck between the plug and the Timesert.
From now on I'll use nylon washers.
Next post should be to report success sometime in the near future.

Ed Wiebe
1990 Westfalia