For maximum low speed output the best solution is to use a larger size alternator like the example shown above which shows the difference between the small case 1G and the large case 1G. Both are 1G series alternators but, the only components that are interchangeable between the two are the pulley, bearings and a few nuts & screws. In almost all cases, the large case alternator will bolt exactly in place of the small case without bracket modification. You can also use the same voltage regulator from your small case alternator to control the large case unit. The only change, is that the large case alternator requires the use of a plug connection, shown below, for the field and stator leads to the alternator.