Getting a car federalized has absolutely nothing to do with what the car has on it. The problem is documenting every thing.
The rules have changed (for the worse) since I was involved with bringing in 30 cars in the early 80's. At the time we had to document with engineering studies each modification. We also had to document all the things that were right such as the AS2 and AS1 glass in all the windows (we had to take pictures of each window label with the chassis number superiposed). The biggest problem is that one can not do this one's self. The current rules require that one must certify a model and then each additional model doesn't have to be individually documented. Just the process needs the documentation. These rules on model certification keep all small timers out of the process. That and the value of the dollar stopped the business almost totally in about 1986.
The fact that the car has a catalyst does not mean that it satifies US requirements. The fact that its cleaner than a US car wouldn't either. What is necessary is US certification. To get this a full body of tests will have to be done, maybe even destructive testing as part of US certification requires longevity issues.
If you wish to do this, find a skilled agent (one currently successful) and get his price. Then evaluate your total cost against what the car will be worth (next to nothing by most accounts).
BTW the reason the car is up for quick sale is probably because it is currently illegal and could be siezed at any minute. It is also likely that it could be siezed even after it was brought into compliance as it obviously was brought into the country illegally. NO CARS can be brought in without a bond being placed against either their removal(as in race cars and/or diplomats/visitors) or compliance. Ask yourself how this car got where you could see it (I am figuring that it isn't still sitting in the freetrade zone).
Bosch Master, ASE Master, L1
33 years MB technician