Spectra lashing instead of moused shackle?

[whimsy]

I've got lines I want to fasten at my masthead using existing fittings. My mast is a carbon fiber pole with a thick aluminum plate on top. The fittings are padeyes through bolted to the bottom of the plate, and ended up with limited clearance between the padeye and the mast. The lines have spliced eyes with SS thimbles.

I found that the shackles I intended to use were too big to fit through the gap between the mast and the padeye. Now I'm looking at smaller shackles, but they don't fit very well through the eyes I spliced on the line, and probably aren't as strong either.

I'm wondering if I could do a lashing with 1/8" spectra cord and get similar results as I would with a moused shackle. It doesn't need to be something quick to undo like the soft shackles I've been reading about--I hope to leave them up with no cause to remove them for a decade.

I don't want this to be the weakest link here, and don't have a compete set of specs, but here's what I can find:

I believe I can buy the same schaefer padeye today, with a 750 lb SWL.
The line is rated at 7,700 or 5,100 lb breaking strength. (two different sizes)

(Yes, I know I'm mixing working load with breaking strength...and don't know what safety factor was used...but they are equivalent around strength if the factor is 7~10. Dunno, but I put them in the same ballpark, with the rope probably being stronger)

If I get 1/8" amsteel it has a 2300 lb (min) breaking strength.

I figure that a lashing with two turns (4 segments) should have 4x2300 lb breaking strength, reduced a bit by any knots and tight turns, but still likely as strong as the other parts. I'm not quite sure how to do that analysis on a lashing, but I figure that three turns (6x2300) is pretty safe.

I've not tied a lashing quite like this before, so I could use suggestions here as well.