Can that be done simply by using a garden hose?

Yes.

I sprayed down both sides of the radiator last night. I also cleaned the K&N filter while I was at it. We'll see on the next 90+ day if that helped. I think I'll be saving my pennies to get the oversized radiator anyway.

I sprayed my radiiator a number of times..even with it out.. and later..a ton of dirt came out... I was amazed.

Perhaps I should get into the habit of spraying it everytime I wash the car.

Over time..that would ensure it'* clean. You want to keep from spraying it when the car is up to temp and the water is cold. That temperature change could have a bad effect on it.

Also keep in mind..when you look at it from the front..you are looking at the AC condensor, not the radiator.

Opps! I did it last night right when I got home, when the temps were up. YIKES! Good to know. I sprayed both sides. The inside is virtually protected by the cooling fans, which makes it difficult to spray. Any advise on how to make it easier? Maybe remove the fans temporarily?

You could remove the fans..you could remove the radiator to get the best possible cleaning.

Which is the lesser of two evils?

keep us updated on that W-Body oversized radiator..
it would be nice to know if it even hooks up - although you would think they would mention that on their webpage -