Re: 6hp johnson year, weight and value?
Judging by the paint and decals it certainly looks like a 1971 model. Model 6R71. It weighs 51 lbs. by itself and would come with a separate 6 U.S. gallon tank by default (1/2 height tank could also have been ordered new).
That one you have in the picture looks pretty good cosmetically. They are great motors, just not too powerful.