Ronstan has a closed body barrel that might be shorter and allow you to pull the rigging tight before runnng out of thread.
Avoid them like the plague or be sure to use Tef gel. Closed body turnbuckles, especially if stainless and not plated bronze, gall like nobodies business.
So it seems then that you are running out of thread even before the ends meet in the middle of the barrel hence your question about a shorter barrel. I hunted around the various turnbuckle suppliers.
http://www.ronstan.us/marine5/saturnbuckles.asp
I am not sure what those are, can you post a link please?Mechanical fittings at the base is a good half measure if your wire is good. Most failures occur at the bottom. They are easy to install.
Thank youhttp://riggingonly.com/himod.htm
I posted that link on the first page. The difference between mechanical and swage is you can put mechanicals on yourself. Mechanicals are superior to swage fittings in all ways.