How much thrust was provided by a typical Meredith Effect radiator?
Here they give a calculation for the thrust generated by a Meredith effect cooler. They do this for the P51 Mustang. It is also mentioned that in Aeroplane monthly, May 1999 (not accessible to me), the designer Atwood claims that the Meredith effects cooler generates 300 lbs of force.

They perform some calculations based on geometry obtained from  Gruenhagen's "Mustang. The story of the P51 fighter", 1969. These calculations also lead to number around 300 lbs (it calculates 270 lbs of thrust).
However, the calculations do not included the effects of the heating of the air whilst passing through the cooler (which is -according to me- a vital component of the way in which these coolers generate thrust).