A single downdraught Webber may well be a good thing, but if you are going to use an original manifold, just be aware that the port size was optimised for the airflow that the original carb allowed & for the air demands of a stock engine in normal use.

If this is to be a pep'ed up grocery getter, you will likely be very happy with it as the manifold is exhaust heated, but it will not be a 10 second car.
Before you declare the conversion a complete success, or a dud, it will be a good idea to get it tuned with the aid of an exhaust sniffer, perhaps even on a dyno, to ensure that it is not running rich or lean at various rev & load conditions. If you can tune the carb properly, it will be a good deal.
Chris