The first braided nylon lines were an attempt to replace silks lines. The taper was in the LINE, like silk and you has to dress them like silk. Later in the 1950’s, somebody had the idea to coat the lines so they wouldn’t have to be dressed and the Cortland 333 was born.
In the early 60’s, Scientific Anglers was founded with their new creation, a fly line with a taper built into the COATING, not the internal core and the modern fly line was born.
What you have pictured appears to be a coated braided nylon line which if it is; it should float. Older braided silk lines and nylon line sizes were based on line diameter NOT weight so the translation between HCH & todays 7wt may be right on the money…or not. The only way to be sure is to try it.
You will probably find the line a lot smaller in diameter than a modern wt., which makes a big difference when it is windy. I don’t know how the old coatings measure up to today’s lines in regards to floating and stiffness so again, the only way to know for sure is to try it.
Worst case, you have a decent intermediate line that may float OK for a few hours if you dress it but will sink as the dressing wears off but don’t knock that because you could use it for nymphing or even dry fly work because the thinner line seems to land and pick-up with less splash IMHO.
Have fun!