Hi Sergio,
I'm new in this forum, but I can assure your is a TR1, your frame number is just 1 more than mine (6140), and is so much probably an '81 model converted, non I explain why: I bought mine (gray with the same tail like your) in Italy, at the end of summer '82, in a big Yamaha dealer near Milano, the bike had the odometer in miles, a trange rear support for a British plate, on the rear swing arm, where the 81 model had the rear fender bearings, there were little prints left by screws, so I suppose stranges manouvres (but not so uncommon in those years) made bye dealer for convert, (sometimes changing decals, plastic parts, or the whole tank with a new season color), a previous year model, for a bike not so successful, and make it more appetizing....
I just saw yesterday night in Milano (a very very rare event!!!) a TR1 of the same color and year like yours, and that model as well, had signs of screws that fixed the previous model of fender, another case of refurbishing...