[TR] Shoulder belts for TR4A

[Chris Kantarjiev]

I'll second the recommendation for Andover - they have a good selectoin
at fair prices.  Wesco Performance is another good choice.

Moss and TRF used to sell Britax retractables that echoed the TR6 
installation - mount the retractor unit low on the wheelarch and
a redirect bracket on top of the wheelarch, mounted via the bolt
that is the "resting point" for the stowed convertible top. 
I don't much care for them; I just use static three points mounted
to the original mounting points and the wheelarch bolt.

The commonly accepted rule about shoulder belts is that the mount
point must be less than 45 degrees from horizontal - not that it
has to be above the shoulder. I prefer to use 30 degrees as the max.