As stated, in the 1980s, Testors became the importer for Italeri and reboxed the kits into the now classic yellow box with a photo of the built up model surrounded by various Testors paint and glue products.
During this time Italeri kits ended up in several companies' boxes. In Germany, you would find Italeri kits in Revell boxes. In Japan, you would find Italeri kits in Tamiya boxes, usually with a Tamiya figure or accessory set added. The last Italeri kit boxed by Tamiya was the Hummer with M242 Bushmaster 25mm gun.
In the mid 80s, Italeri hit their peak with kits like the M47 Patton, Leopard 1A2, Willys Jeep, M24 Chaffee and several Sherman based kits . Also issued in the yellow boxes were some fairly old Japanese models made by Peerless Max that Italeri had acquired. These included the US 155mm gun, 1½ ton Dodge, White Scout Car, and the WC Dodge Ambulance, Beep, Anti-tank Dodge, and Staff Car. Not bad kits, but not as good as the newer Italeri kits.
You will see some of those kits in Bilek boxes and Zvezda boxes as well.
Today, Testors still imports Italeri kits. They just leave them in the original boxes and add a sticker on the box end with Testors Corp. info on it.