If you can get Mikes idea to fly would be a good one. If not, then you wil have to do as I did importing from Australia. You have several options on the form. One is if you are basicly a diplomat. The ones that aply are one of two. You can import the car without the engine and trans in the car.They can be in the same container, just not in the car. It come in as parts. Then you have to asses a value, and you pay a tax based on that value. Word of warning, don't low ball it too much, as it will raise some red flags.
With the second, if it is in the car you will have two choices again. The first you have to meet DOT safety regs for the year of manufacture, which means 5 MPH bumpers, airbags and all the other safety features of that year. The other option is to import it as a race car. This one says you can bring it in but you can't drive it on the road, only closed events, or off road. My seller either forgot, or was just stupid and left the motor in. Fortunately for me, I had him put some race stickers on the car and we imported it that way. They didn't tell me that the motor was in the car til it was 3/4 the way to the US. My only other alternative was to ship the car out of the country, pull the engine and trans, and then reship it back into the country. So I filled out the forms for a race car.
You are supposed to let them know if the cars status changes, but bureaucracy being what it is, the right hand doesn't tell the left hand what it is doing, and you can register the car later on. For me it has been almost 5 years, My local tag office(Ga.) told me that for the receipt to act as a bill of sale, I would have to find a police officer who would sign off on the I D of the car(VIN) as a valid VIN #. They go through Interpol to check if it is stolen, and that is it. I just have to pay the back taxers for the 5 years. Since it is listed as a 65 Ford GT, the taxes are about $25 a year. I can get a historical tag, regular tag, or prestige tag, which is what I plan on doing.
Your best bet to register the car is to check with the Texas DOT. Maybe one of the Texans can chime in on that.
Bil