The box is a little confusing - to me that shows a watch with a 404/3641 case but a Carrera dial too. Maybe that was the original plan and the case was redesigned without the boxes being reprinted. Stranger things have definitely happened in the world of vintage watches!

There are some things the brochures do agree on though, that the 3641 has a chrome case - these early Carreras are all stainless steel, gold-plated steel or 18K gold.

The later brochure that Jarl linked has the 3641 shown as a separate model from the Carreras. The earlier one has it separate from the 404.

However, to muddy the waters a bit, the earlier brochure I linked insists that the 3641 only has a "white" dial (these are referred to as white, but are actually silver, I don't know why they call them white...) and Jarl's brochure also only mentions a white dial. Now, we see lots of dial variations that never made the brochures (the white-on-black and black-on-white Carreras are perfect cases in point) but it is quite unusual for them to be specific about there only being one dial variation.

There is the case shape too. A black Carrera 45 should be in the case below:

Jarl's brochure shows the difference between the 3641 case and the Carrera 45 Dato immediately below very well. There are some minor differences between a 45 Dato case and a "standard" 45 case but these are more about depth to house the different Landeron and Valjoux movements.

All the Carrera 2447/8s, 3647/8s, 3147s and 7753s I have seen have been in variations of this case with the angular lugs. We do see some difference in cases - there was a lot of discussion here recently over the "fat lug" version of the 2547 Carrera 12 Dato case, which we got some inside information was genuine. It's not unusual for companies at the time to switch case supplier during a production run, accounting for some of the variation. Even allowing for that, I personally would only be comfortable going for a Carrera in the case I am familiar with, with the angular, bevelled lugs.