With a carburetor or TBI setup, the intake manifold must have enough heat to prevent icing internally. Volvo's PV544 manifold had intake/exhaust sides "bonded" together (B18D SUs), so exhaust heat warmed up intake side.
Looking at the "Weber" DGV intake manifold for Volvo B18/B20, I don't know if icing happens in colder environments. Years ago, I recall a person with an aftermarket intake manifold having this icing issue in a PV544.
Pilot's tip of the week...Carb Ice In Summer?
It is possible for the temperature drop in the carburetor to be as much as 70 degrees Fahrenheit, meaning that ice could form on a day where the ambient temperature could be as much as 100 degrees Fahrenheit. However, carburetor ice is most likely to form when temperatures are below 70 degrees Fahrenheit and the relative humidity is more than 80%
Using a Weber Retroject 38/38 downdraft Throttle Body is a nice idea, but icing would be a topic to consider.