A lot of the answers refer to an A65 which you do not have, as you can see from the pics below the battery tray on a B44 3 bolts drop down to a couple of support brackets which stop you mounting boxes below the battery tray unless they fit between the 2 brackets plus it does get mucky there. I mount the regulator where the orginal rectifier went which is behind the toolbox where the red wires are exiting your harness (which I use for the earth for the regulastor), I also fit the capacitor in the same area. Unless you are fitting an oversize capacitor like I do there should also be enough room to fit the electronic ignition, downside is to get to the boxes the seat has to come off by loosening the 2 top shock bolts. I prefer the electronic box to be near the coil (or coils if twin sparked) so go for the gussets behind the headstock but it can go further back as the wires from the timing chamber normally run back to the orginal postion for the now redundant points condensor just up from the rear engine mounting bolt.
I am reading elsewhere to discard the battery eliminator. I already have a battery anyway and plan to keep it in that configuration. Some say the B.E. may cause damage to other electrical components like the rectifier.
1969 BSA B44VS PC8113 Engine PC8113B44VS Recently acquired (Feb 2011) Aiming to get running and return all parts/configurations to original. First BSA. Have 1970 Honda CB750 too.