Based on the Orange, CA decal, you have my vote that the blank is very early Sila-flex. For a custom rod, I would not make too much about hardware comparisons (as long as it is within period versus later).
Allow me to quote myself from earlier in the thread about the first rod presented:
Sila-flex did not sell finished/completed rods until the 1952 catalog. First they sold only blanks (1949 Catalog), then kits (ferruled) were added (1950 Catalog). Observe also the trademark registration (from Orange, CA, not Costa Mesa - did you miss that part?) is for blanks, not rods. I think this rod was custom wrapped and one shouldn't make too much of the wrapper's choices - other than recognizing a custom wrap.
One thing though, I feel like I’ve missed something in the information I carry with me. You write, “… similar to Fenwicks of the era.” There was Fenwick in the late 1940’s?
I don’t know when Sila-flex switched to a Costa Mesa decal. It’s possible it was prior to your 5/10/50 rod assembly, if an in stock much earlier blank was used.
Out of curiosity, what is the distance between the 1,2,3, … markings on the rod?