Bill,
It's times like these when folks realize how important the surveys I send them are. As you can see from our M38 data base on the Yahoo site we don't have a lot of USAF hood numbers to interpolate with.
At any rate my feelings are if you're not positive what the original hood number was then don't try to fudge in a number that will skew any future attempts to establish an accurate data base. Instead simply use the first 3 or 4 digits of the closest hood number and add your serial at the end. This will become obvious to researchers years from now trying to sort out hood numbers.
As an aside the USAF did not start using their own version of registration numbers untill 54 or so. Therefore unless you intend to portray an M38 in use by the USAF after 1954 the original Army hood number sequence would be correct.
Here's an example of a USAF M38 when the USAF still used the Army hood number.
The next transition was to drop the Army's 209 prefix which just ID's vehicle type and use the USAF letter designation for vehicle purpose and the last 5 digits of the original Army hood number. Thus in this example you can see the original hood number on the side of the hood has been painted out with Strata Blue and the A-12273 entered on the hood. You'll also note that the earlier full registration number under the word USAF on the door sill area has also been painted out.
And finally the USAF starts procuring under their own contracts and here is how they did it for those. One note here, I have seen these jeeps built on USAF contract with the numbers on the aft end of the hood side, on the cowl and on doors (hard top models). The year of the contract followed by the letter designator for vehicle purpose and then the registration sequence number.
