As stated, unless you have an alternator B31, you don't want a regulator rectifier. You need a dynamo voltage regulator and there is no better than Manormike's DVR2 as many members here can testify. However, if you do have a late engine in there with an alternator (and coil ignition), then you might well need a reg/rect and the Podtronics unit available from Paul (Norbsa) Goff is perfect. 6v ones cost twice what 12v ones cost though, and then you still can't buy 6v bulbs easily.
If you want a B31 wiring diagram, either dynamo or alternator, come back on here and stuff can be sorted. But even the basic Haynes cheapo lousy book has diagrams for both.
Best of luck.
