Wouldn't do it. Takes years of climbing experience on different species of conifers to get a sense of what will hold you and what won't. Every conifer species has it's own strength characteristics. Beyond that you need to do visual inspection, there can be defects hard to see, takes experience and skill to do it.
Have no idea what species, height of first branch etc. you're talking about, every conifer is different. No way I'd do an 70 ft. ascent on a 2" diameter conifer branch (for example)
Best strategy for tall conifers in general is to climb SRT, put the rope through the crown over multiple branches and anchor the other end on the ground (trunk of same tree of another tree nearby). That way you can take advantage of several branches to hold your weight.
-moss