78 RD400 like this but orange
I had several RD350's and RD400's.
That looks like a '76 to me.
I thought that orange was a '75 RD350 (I had one. VERY fast!), '76 400 was blue. '77 400 was Red (had 2 of them). '78 was gray or silverish, if I remember correctly. '79 was the Daytona Special (had one!!! shoulda kept that bad boy).
I am pretty sure I have the above correct. Unless Yamaha had multiple colors in given years.
edit: now I am remembering the tank graphics were larger in '76. This one has graphics like my 2 red 77's. So, maybe '78 had blue and silver.