Twin-row radials were offset. Same for the 4 row 4360.
Cowling on most piston engines is crucial for ensuring proper cooling. A few radial installations leave the engines completely exposed, and this is usually done only on single-row installations. A few utilize a pressure ring, a few simple pistons just use eyebrows or baffles, but most installations use pressure cowls with baffling to control airflow for maximum cooling. In most cases, cowl flaps are also used to vary the airflow and increase cooling when needed.
* Didn't the twin-row radials have a cylinder offset as well?
Yes.
* Why didn't they think of that earlier -- the idea isn't exactly a leap of imagination as it would simply be an extension of the twin-row radials?
They did think of that earlier. Offset cylinder rows are a basic design feature of radial engines.
The 4360 used a gradual offset to the right, or clockwise, as seen from the front, with airflow spiraling clockwise aft. An intricate baffling system and induction system was used to provide what limited airflow there was, to reach the rear cyclinders. The whole package was a royal pain in the butt when it came to changing a cylinder, which is a very common act on old, large radial engines.