OK. The smaller wire is supposed to be 6.0 so if you can strip them far enough back you could blend the strands of both, and the areas would add. (31 mm^2) Use the conversion to get AWG, but keep in mind the insulation may make the strand hard to blend into a circle. Then you can tell us how well they work.

If I made the investment in one of these, I'd probably pick the larger one, and if it wouldn't tighten on the OE wires, I'd stuff some more in to make up. Sealing shrink sleeving with a thick wall is a consideration. I bet the marine stores have stuff like this. One in Florida sends me specials every week since I bought some vacuum hose from them 10 years ago. Sherco.
--
Art Benstein near Baltimore

If you have a lot of tension and you get a headache, do what it says on the aspirin bottle:
"Take two Aspirin" and "Keep away from children"