I would go with a modern alternator, but you have to go to Negative earth!
I used a alternator from a diesel engine, that had a output shaft.
I did some modification to connect the steering pump to the back of the alternator.
Is running ok for more that 15 Years now
Update: I have replaced old dynamo with a Positive Earth Alternator. Wiring done as per instructions - Battery wire from old regulator connected to large terminal, small terminal connected to WL (warning light or ignition light), followed by a relay fitted in between ignition light and ignition. Car starts well, checked charging its giving 14.4 volts - so charging is good. However the ignition light is off and amp meter is not moving. Now I have to do some more research into this problem. But at least the Alternator is working and battery is being charged.... !
Thanks Barrie. After fitting the +ve earth alternator, the battery is being charged - no problems - but the ignition light is completely off - I'm in touch with the seller and hopefully will find a solution to it. Thanks Rashid