If you carry out the Volvo Radiator modification using a second-hand radiator with plastic side tanks, there is a chance that the temperature sender unit may leak. This is located in the top of the driver's side plastic tank as shown below.
The sender unit, when not fitted, has a blanking plug to fill the hole. There is a rubber grommet which fits here to seal the blanking plug and it softens with age. The correct Volvo spare part for this no. 1378869 ("Rubber Bushing" - I paid only $2.75 for one of these from Manning Valley Motors at Taree).
Unfortunately, when it failed at Mungo Brush, I had no spare and needed to improvise. The repair below works fine for a temporary seal of the 3/4" hole.

The plastic blanking plug back in place. None of this is required if you use the brass tank radiator.

These bits came from my spare parts odds & ends that I carry. The hose is about 1/2" ID (might have been ex. brake booster?) and the bolt is 2" x 3/8".

This is it assembled. Push about 1/2" of the left hand end into the hole and tighten the nut on the engine compartment side. (I did it back-to-front with the potential disaster of losing the nut inside the radiator when removing it)

The head of the bolt pulls in to the tube ...

... gradually expanding it. You need to hold it such that the expanded bit fills the hole in the plastic tank.