No argument there. Since he already has your LED regulator board in-hand, that only requires re-wiring the harness but no additional out-of-pocket cost. Sounds like a plan.
I was suggesting an approach using just the existing 6V regulator output that is already driving (apparently) some existing 6V bulbs. This method would require soldering in 2 resistors which would involve some out-of-pocket cash if his parts cupboard is bare.