On Tuesday, June 7, 2016 at 5:42:31 AM UTC-7, Robert M wrote:
...Since your glider is type certificated you need to be very careful
about modifications to anything.

Note that here in the US, there are provisions for the installation of owner-produced parts installed in certificated aircraft by A&P mechanics. This article describes the process, but serves as a cautionary tale about doing it carefully:

http://150cessna.tripod.com/parts.html

Also, I helped install an aluminum E-size cylinder last winter, and I can say that at least some of them do have necks. But Robert Mudd raises a good point that they are not as long or as sharply defined as on the older steel cylinders.

Thanks, Bob K.