Thanks. I would enjoy seeing your version of the mod.
Regarding 6V with 2x26350 vs 3V with 1x26650: the available 26350 cells have more than double the IR of the good 26650 cells, but because half the current is needed for the same output, you will get comparable performance because the greater circuit resistance multiplied by the reduced current gets you a similar voltage drop.
Djozz, I don’t know if you saw my thread about calculating current in direct drive setups. Along with your forward voltage measurements one can predict the current flow in these different setups.
For example, with 2x26350 cells with 0.072 ohms IR each: about 6.5A will flow through an XHP50 with fully charged cells.
About 8A should flow through an XHP70 with the 2x26350, so this is actually higher performance than my 3V XHP70, which flows 13.7A.