Interesting how a post asking about brackets gets so far off. Me included.

To summarize on topic. Brackets are available as posted. DIY brackets are fairly easy to design and build.

It is unarguable to stay with 6V/generator except for nostalgia.
Not cheaper, not more reliable, more hassle to find parts. More wiring. More voltage drop. Less output.

Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn