Thanks to Dean's info, I was able to proceed and do the conversion.
The new unit is half the size of the generator and looks like a factory fit. there is no "idiot light" but it is a simple matter to add a hidden digital voltmeter.


Alphatech

How to install one wire mini Denso type one wire alternator on a Volvo B18.

First disconnect the wiring and remove the existing 12 volts Bosch generator, the wiring will not be required for the new installation, just tuck it away out of sight.

Next, remove the generator bracket from the engine block together with the mounting bolts and vibration bushings. You will need to make a new bracket, longer in the front, to hold the mini unit and align the pulley.
{Use the bracket as a template for the shape and hole sizes / location on the new bracket,the rear mounting point is not needed.} I used a piece of hardened steel, approx. 8.5” long, and bent the front right angle so that the measurement from the front bracket hole center to the front face of the alt. mounting right angle was 2.5”

Be sure to shape the right angle lower part the same as original, so that it does not interfere with the bottom radiator outlets or hose.
The Alt. mounting hole needs a ⅜” clearance bolt hole. Secure the Alt. with a ⅜”x 1 ¾” fine thread bolt, washers and locknut.
My choice was a Denso 1 wire 35 amp mini alternator from DB Electrical. Part # 400- 52062 It works perfectly. The DB folks were a pleasure to deal with and the price was good.

Higher outputs are available, but some may require additional ignition inputs.