I have installed lower handlebars on my XV920R (same as the '81 TR1) and I just spent about four hours at the local bike shop searching for a shorter clutch cable.  Success!  The clutch cable off a 1987 to '99 YFZ 350 is about 15cm shorter than the original cable and has exactly the right fittings on both ends.  Perfect fit!  The SPI (Motion Pro) part number is 05-116.
This may be of value to someone else.