The width of my sample of the Kato chassis "under the bonnet" comes out to 11.9mm. The inside LENGTH of your original model was perfect for the Kato chassis. There are four small tabs, two forward, two aft; and these rested very nicely on the pads in the model.
I never tried the Lifelike chassis with this model, but as you noted, the pickup arrangement is difficult to deal with. The Kato is more expensive, but more durable and it runs better than the Lifelike. I guess now I need to order another body. Thanks! Respectfully, Bob S.